ACS Physical Chemistry Thermochemistry Study Guide – Flashcards
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The entropy of a perfect crystal is zero.
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What is the third law of thermodynamics?
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As a whole, the universe always tends towards increasing entropy.
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What is the second law of thermodynamics?
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More microstates = higher entropy
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What is the relationship between number of microstates and entropy?
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Temperature increases, entropy increases (direct)
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What is the relationship between temperature and entropy?
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Heavier = increased entropy (direct)
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What is the relationship between atomic weight and entropy?
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Entropy increases
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What happens to entropy when a substance is dissolved in another?
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When moles of gas increase, entropy increases (direct)
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What is the relationship between moles of gas and entropy?
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deltaG(system)=deltaH(system)-TdeltaS(system)
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What is the relationship between free energy, enthalpy, and entropy?
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The extent of the spontaneity of a process, and the useful energy available from it
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What does change in G measure?
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Spontaneous processes produce work
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What is the relationship between work and spontaneous processes?
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Non-spontaneous processes require work
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What is the relationship between work and non-spontaneous processes?
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Work is being produced - spontaneous
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What does -w mean?
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Work is required - non-spontaneous
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What does a positive sign for w mean?
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No
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Can a change be spontaneous in both directions?
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Value depends on the amount of substance
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What is an extensive property?
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Non-spontaneous process - requires work
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What does ?G > 0 mean?
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Spontaneous process - produces work
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What does ?G < 0 mean?
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The free energy change that occurs when 1 mole of a compound is made from its elements
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What does standard free energy of formation mean? ?Go
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Changes its sign
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What does reversing a reaction do to the standard free energy of formation? ?G0
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Because the large negative ?H/large energy release makes the free energy change negative.
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Why are most exothermic reactions spontaneous?
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The reaction occurs spontaneously at all temperatures or at none.
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What happens when ?H and ?S have opposite signs?
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Spontaneous at all temperatures, negative free energy
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What happens when enthalpy (?H) is negative and entropy (?S) is positive?
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Negative ?H, positive ?S
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What is the likely sign of ?H and ?S for a combustion reaction?
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Nonspontaneous at all temperatures
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What happens when ?H is positive and ?S is negative?
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Reaction becomes spontaneous as temperature increases
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What happens when ?H and ?S are both positive?
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Reaction becomes spontaneous as temperature decreases
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What happens when ?H and ?S are both negative?
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Because such an irreversible process will always involve some free energy being converted to heat
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Why can the maximum work of a system never obtained from a real process?
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Set ?G equal to zero and solve -- use T=deltaH/deltaS to find the temperature value.
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How do you find where a reaction becomes spontaneous?
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Spontaneous
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Is a chemical reaction proceeding to equilibrium a spontaneous or non-spontaneous change?
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?G0 reaction proceeds to the left
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How to determine reaction direction from ?G?
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To the left / to reactants
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Which direction does the reaction proceed if ?G is positive?
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To the right/ to products
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Which direction does the reaction proceed if ?G is negative?
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Positive ?S(system) means available microstates increases/disorder increases
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How to predict ?S(system)? (change in entropy of a system)
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1. Write the balanced chemical equation with the proper coefficients that make the product ONE MOLE. 2. Find the value of the one mole of product in Appendix B. This is the deltaS(standard) for the product. 3. Find the value of the reactants in Appendix B for deltaS(standard) and multiply them by the coefficients you got in step 1. 4. Use total = products-reactants for your final value.
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How to calculate the ?So (aka standard entropy change) of the formation of one mole of gas from its elements?
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?G=?H-T?S
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How to calculate ?G (free energy) using enthalpy ?H and entropy ?S values?
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?G=-RT ln K
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What is the equation that relates ?G to K?
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ln(# of microstates)
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What is the Boltzmann constant?
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More microstates
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What does a big W mean?
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Big ?S - more entropy
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What does more microstates mean?
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Smaller ?S - less entropy
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What does fewer microstates mean?
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Microstates increase, entropy increases
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What happens to entropy when volume is increased?
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?S(system)=qrev/T
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What is the relationship between ?S of a system, q, and T?
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It increases
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What happens to entropy ?S when temperature increases?
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As mass increases, entropy increases
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What is the relationship between mass and entropy ?S?
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As molecular complexity increases, entropy increases
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What is the relationship between molecular complexity and entropy ?S?
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?G=RTlnQ
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What is the relationship between ?G and Q?
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It gets smaller
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What happens to K as ?G becomes more positive?
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It gets bigger
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What happens to K as ?G becomes more negative?
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Reaction proceeds to the left/reactants
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What direction does a reaction proceed if ln Q/K is positive?
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Reaction proceeds to the right/products
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What direction does a reaction proceed if ln Q/K is negative?
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property which is directly proportional to the size of the system (i.e.. V, m, E )
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Extensive Property
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property which does not depend on the size of the system (i.e. P, T, density, molar volume)
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Intensive Property
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a reflects how strong the molecules attract each other (IM forces); b reflects the size of the molecule --- van der Waals equation extends beyond the ideal gas law to take into account attractive and repulsive forces
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van der Waals constants
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plot of P as a function of molar volume at constant temperature
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Isotherm
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Law which states "all gases have the same properties of they are compared at corresponding conditions"
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Law of Corresponding States
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temperature at which repulsive and attractive interactions cancel and the gas appears to behave ideally
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Boyle Temperature
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the manner of energy transfer that results from temperature difference between system and surroundings ("unorganized motion")
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Heat (q)
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the transfer of energy between system and surroundings as a result of existence of unbalanced forces between the two ("organized motion")
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Work (w)
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property that depends on the state of the system, and not upon the history of the system (i.e. energy, entropy)
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State Function
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when pressure the pressure exerted on the system and the pressure of the system differ only infinitesimally so slight changes are able to be made
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Reversible Process
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property that depends on the path taken to reach the state of the system
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Path Function
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process which no energy as heat is transferred (dq = 0 ; therefore, dU=dw )
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Adiabatic Process
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total heat content of a system; it is equivalent to the internal energy plus the products of pressure and volume
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Enthalpy (H)
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the heat involved in a combustion reaction --chemical reactions that absorb heat ( dH > 0) are called endothermic --chemical reactions that release heat (dH <0) are called exothermic
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Heat of Combustion
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unavailability of a system's thermal energy for conversion into mechanical work, often interpreted as the degree of disorder or randomness in the system ---dS=0 for cyclic processes or reversible processes in isolated system ---dS > 0 for spontaneous processes in isolated systems
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Entropy (S)
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= U - TS ---will decrease during any spontaneous process that occur at constant T and V and will achieve its minimum value at equilibrium
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Helmoltz Energy (A)
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= H - TS = A + PV ---will decrease as a result of any spontaneous process until the system reaches equilibrium
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Gibbs Energy (G)
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thermodynamic property which described the deviations of ideality; the ratio f/p is the coefficient
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Fugacity
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F = C - P + 2 ---Phase (P): numer of phases ( P=1 is for within a region, P=2 is for on the coexistence curve, P=3 is for at the critical point) ---Component (C): chemically independent variable describing how many components are in the system ---Degrees of Freedom (F): number of intensive variables we can change yet still be in the same phase
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Gibbs Phase Rule
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a mixture for which there is no change in composition upon boiling (not possible to achieve separation)
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Azeotrope
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property which depends only on the number of solute particles present, not on their identity (i.e. vapor pressure, boiling point, freezing point, osmotic pressure)
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Colligative Property
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--- at equilibrium dG=0 ; Qp=Kp --- If Qp < P: dG P: dG >0 so reaction is moving R to L
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Reaction Quotient (Q) vs. Equilibrium Constant (K)
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Contains some particles that are intermediate in size between the small particles in a solution and the larger particles in a suspension
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Colloids
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Fifth state of matter that exists at extremely low temperatures and atoms behave as a single particle
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Bose-Einstein Condensate
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Result of force distributed over an area
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Pressure
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The volume of a gas is directly proportional to its temperature in kelvins if the pressure and the # of particles of the gas are constant
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Charles's Law
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The volume of a gas is inversely proportional to its pressure if the temperature and the # of particles are constant
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Boyle's Law
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The system absorbs energy from its surroundings
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Endothermic
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The energy a substance must absorb in order to change from a solid to liquid
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Heat of Fushion
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The system releases energy to its surroundings
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Exothermic
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When a gas changes directly to a solid
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Deposition
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When a solid changes directly to a gas
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Sublimation
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The elements in group 2A; differences shown by reactivity to water
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Alkaline Earth Metals
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The elements in group 7A; highly reactive nonmetals
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Halogens
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The elements in group 8A; colorless odorless and extremely unreactive
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Noble Gases
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An ion with a negative charge
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Anion
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An ion with a positive charge
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Cation
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A covalent bond in which electrons are not shared equally
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Polar Covalent Bond
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pressure, volume, temperature, and amount of substance: p = f(T,V,n).
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2. An equation of state interrelates
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permits the passage of energy as heat.
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6. A diathermic boundary is a boundary that
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prevents the passage of energy as heat.
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7. An adiabatic boundary is a boundary that
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no change of state occurs when two objects A and B are in contact through a diathermic boundary.
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7. Thermal equilibrium is a condition in which
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if A is in thermal equilibrium with B, and B is in thermal equilibrium with C, then C is also in thermal equilibrium with A.
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8. The Zeroth Law of thermodynamics states that
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T/K = ?/°C + 273.15.
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9. The Celsius and thermodynamic temperature scales are related by
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pV = nRT, exactly under all conditions.
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10. A perfect gas obeys the perfect gas equation
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pressure exerted by a mixture of gases is the sum of the partial pressures of the gases.
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11. Dalton's law states that the
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p_J = x_J p, where x_J = n_J/n is its mole fraction in a mixture and p is the total pressure.
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12. The partial pressure of any gas is defined as
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B, C, . . . : pV_m = RT(1 + B/V_m + C/V^2_m + · · · ).
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13. In real gases, molecular interactions affect the equation of state; the true equation of state is expressed in terms of virial coefficients
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pressure of a vapour in equilibrium with its condensed phase.
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14. The vapour pressure is the
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volumes at each end of the horizontal part of the isotherm have merged to a single point. The critical constants p_c, V_c, and T_c are the pressure, molar volume, and temperature, respectively, at the critical point.
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15. The critical point is the point at which the
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dense fluid phase above its critical temperature and pressure.
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16. A supercritical fluid is a
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approximation to the true equation of state in which attractions are represented by a parameter a and repulsions are represented by a parameter b: p = nRT/(V? nb) ? a(n/V)^2.
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17. The van der Waals equation of state is an
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the actual variable divided by the corresponding critical constant.
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18. A reduced variable is
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the same reduced pressure.
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19. According to the principle of corresponding states, real gases at the same reduced volume and reduced temperature exert
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outside the system where we make our measurements.
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2. The system is the part of the world in which we have a special interest. The surroundings is the region
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transferred.
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3. An open system has a boundary through which matter can be
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cannot be transferred.
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3. A closed system has a boundary through which matter
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neither matter nor energy can be transferred.
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3. An isolated system has a boundary through which
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do work. The internal energy is the total energy of a system.
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4. Energy is the capacity to
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dw = ?Fdz . Heat is the transfer of energy as a result of a temperature difference between the system and the surroundings.
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5. Work is the transfer of energy by motion against an opposing force,
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releases energy as heat to the surroundings.
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6. An exothermic process
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absorbs energy as heat from the surroundings.
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6. An endothermic process
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the current state of the system and is independent of how that state has been prepared.
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7. A state function is a property that depends only on
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the internal energy of an isolated system is constant, ?U = q + w.
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8. The First Law of thermodynamics states that
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dw = ?p_exdV. The work of free expansion is w = 0.
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9. Expansion work is the work of expansion (or compression) of a system,
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w = ?p_ex?V.
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9. The work of expansion against a constant external pressure is
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w = ?nRT ln(V_f /V_i).
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9. The work of isothermal reversible expansion of a perfect gas is
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can be reversed by an infinitesimal modification of a variable.
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10. A reversible change is a change that
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reversible change.
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11. Maximum work is achieved in a
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heat transfers during physical and chemical processes.
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12. Calorimetry is the study of
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C_V = (?U/?T) _V.
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13. The heat capacity at constant volume is defined as
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C_p = (?H/?T) _p.
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14. The heat capacity at constant pressure is
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C_p ? C_V = nR.
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14. For a perfect gas, the heat capacities are related by
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H = U + pV.
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14. The enthalpy is defined as
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energy transferred as heat at constant pressure, ?H = q_p.
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14. The enthalpy change is the
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T_f = T_i(V_i/V_f)^(1/c), c = CV,m/R. The pressure and volume are related by pV^? = constant, with ? = C_p,m/C_V,m.
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15. During a reversible adiabatic change, the temperature of a perfect gas varies according to
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change in enthalpy for a process in which the initial and final substances are in their standard states. The standard state is the pure substance at 1 bar.
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16. The standard enthalpy change is the
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?_subH® = ?_fusH® + ?_vapH® .
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17. Enthalpy changes are additive, as in
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?forwardH® = ??reverseH®.
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18. The enthalpy change for a process and its reverse are related by
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standard reaction enthalpy for the complete oxidation of an organic compound to CO2 gas and liquid H2O if the compound contains C, H, and O, and to N2 gas if N is also present.
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19. The standard enthalpy of combustion is the
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sum of the standard enthalpies of the individual reactions into which a reaction may be divided.
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20. Hess's law states that the standard enthalpy of an overall reaction is the
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standard reaction enthalpy for the formation of the compound from its elements in their reference states. The reference state is the most stable state of an element at the specified temperature and 1 bar.
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21. The standard enthalpy of formation (?_fH® ) is the
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?_rH® =?Products ??fH® ??Reactants ??fH® .
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22. The standard reaction enthalpy may be estimated by combining enthalpies of formation
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?_rH® (T2) = ?_rH® (T1) + Integral (T2 to T1) ?_rC® pdT.
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23. The temperature dependence of the reaction enthalpy is given by Kirchhoff's law
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infinitesimal quantity that, when integrated, gives a result that is independent of the path between the initial and final states. An inexact differential is an infinitesimal quantity that, when integrated, gives a result that depends on the path between the initial and final states.
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24. An exact differential is an
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?_T = (?U/?V) _T . For a perfect gas, ?_T = 0.
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25. The internal pressure is defined as
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cooling of a gas by isenthalpic expansion.
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26. The Joule-Thomson effect is the
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? = (?T/?p) _H.
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27. The Joule-Thomson coefficient is defined as
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?_T = (?H/?p) _T = ?C_p?.
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27. The isothermal Joule-Thomson coefficient is defined as
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temperature at which the Joule-Thomson coefficient changes sign.
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28. The inversion temperature is the
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The entropy of an isolated system increases in the course of a spontaneous change: ?S_tot > 0.
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2. The Second Law in terms of entropy:
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dS = dq_rev /T.
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3. The thermodynamic definition of entropy is
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S = k lnW.
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4. The statistical definition of entropy is given by the Boltzmann formula
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sequence of isothermal and adiabatic reversible expansions and compressions.
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4. A Carnot cycle is a cycle composed of a
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? = |w|/q_h.
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5. The efficiency of a heat engine is
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?_rev = 1 ? T_c /T_h.
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5. The Carnot efficiency is
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dS ? dq/T.
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7. The Clausius inequality is
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two phases are in equilibrium at 1 atm.
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8. The normal transition temperature, T_trs, is the temperature at which
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?_trsS = ?_trsH/T_trs.
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8. The entropy of transition at the transition temperature is
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many normal liquids have approximately the same standard entropy of vaporization (about 85 J K?1 mol?1).
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9. Trouton's rule states that
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S(T_f) = S(T_i) + Integral (T_f to T_i) (C_p /T)dT.
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10. The variation of entropy with temperature is given by
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area under a graph of C_p /T against T, using the Debye extrapolation at low temperatures, C_p = aT3 as T?0.
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11. The entropy of a substance is measured from the
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approaches zero as the temperature approaches zero: ?S?0 as T?0 provided all the substances involved are perfectly ordered.
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12. The Nernst heat theorem states that the entropy change accompanying any physical or chemical transformation
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The entropy of all perfect crystalline substances is zero at T = 0.
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13. Third Law of thermodynamics:
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?_rS® =?Products ?S® m -?reactants ?S® m .
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14. The standard reaction entropy is calculated from
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S* (H+, aq) = 0 at all temperatures.
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15. The standard molar entropies of ions in solution are reported on a scale in which
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A = U ? TS.
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16. The Helmholtz energy is
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G = H ? TS.
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16. The Gibbs energy is
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(a) dS_U,V ? 0 and dU_S,V ? 0, or (b) dA_T,V ? 0 and dG_T,p ? 0.
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17. The criteria of spontaneity may be written as:
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dA_T,V = 0.
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18. The criterion of equilibrium at constant temperature and volume,
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dG_T,p = 0.
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18. The criterion of equilibrium at constant temperature and pressure,
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w_max = ?A.
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19. The maximum work and the Helmholtz energy are related by
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w_add,max = ?G.
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19. The maximum additional (non-expansion) work and the Gibbs energy are related by
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?_rG® = ?_rH® ? T?_rS® =?Products ?G® m -?reactants ?G® m .
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20. The standard Gibbs energy of reaction is given by
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standard reaction Gibbs energy for the formation of a compound from its elements in their reference states.
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21. The standard Gibbs energy of formation (?_fG®) is the
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?_fG®, ?_rG® =?Products ??fG® ??Reactants ??fG®.
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22. The standard Gibbs energy of reaction may be expressed in terms of
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?_fG® (H+, aq) = 0 at all temperatures.
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23. The standard Gibbs energies of formation of ions are reported on a scale in which
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dU = TdS ? pdV.
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24. The fundamental equation is
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.
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25. The Maxwell relations are
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expression for pressure in terms of thermodynamic quantities, ?_T = T(?p/?T) _V ? p.
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26. A thermodynamic equation of state is an
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dG = Vdp ? SdT.
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27. The Gibbs energy is best described as a function of pressure and temperature,
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(?G/?p) _T = V and (?G/?T) _p = ?S.
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27. The variation of Gibbs energy with pressure and temperature are, respectively,
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(?(G/T)/?T) _p = ?H/T2.
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28. The temperature dependence of the Gibbs energy is given by the Gibbs-Helmholtz equation,
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G(p_f) = G(p_i) + V_m?p. For a perfect gas, G(p_f) = G(p_i) + nRT ln(p_f/p_i).
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29. For a condensed phase, the Gibbs energy varies with pressure as
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uniform throughout in chemical composition and physical state.
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1. A phase is a form of matter that is
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equilibrium.
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2. A transition temperature is the temperature at which the two phases are in
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thermodynamically unstable phase that persists because the transition is kinetically hindered.
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3. A metastable phase is a
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regions of pressure and temperature at which its various phases are thermodynamically stable.
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4. A phase diagram is a diagram showing the
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line separating the regions in a phase diagram showing the values of p and T at which two phases coexist in equilibrium.
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5. A phase boundary is a
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pressure of a vapour in equilibrium with the condensed phase.
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6. The vapour pressure is the
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free vaporization throughout the liquid.
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7. Boiling is the condition of
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vapour pressure of a liquid is equal to the external pressure.
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8. The boiling temperature is the temperature at which the
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disappears and above which a liquid does not exist whatever the pressure. The critical pressure is the vapour pressure at the critical temperature.
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9. The critical temperature is the temperature at which a liquid surface
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dense fluid phase above the critical temperature.
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10. A supercritical fluid is a
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coexist in equilibrium.
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11. The melting temperature (or freezing temperature) is the temperature at which, under a specified pressure, the liquid and solid phases of a substance
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the three phase boundaries meet and all three phases are in mutual equilibrium.
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12. The triple point is a point on a phase diagram at which
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molar Gibbs energy of the substance.
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13. The chemical potential ? of a pure substance is the
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uniform throughout a system at equilibrium.
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14. The chemical potential is
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(?? /?T) _p = ?S_m and with pressure as (?? /?p) _T = V_m.
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15. The chemical potential varies with temperature as
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p = p*e^(V_m?P/RT).
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16. The vapour pressure in the presence of applied pressure is given by
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dp/dT = ?_trsS/?_trsV.
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17. The temperature dependence of the vapour pressure is given by the Clapeyron equation,
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d ln(p/dT) = ?_vapH/RT^2.
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18. The temperature dependence of the vapour pressure of a condensed phase is given by the Clausius-Clapeyron equation,
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phase transitions based on the behavior of the chemical potential.
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19. The Ehrenfest classification is a classification of
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change in volume per mole of A added to a large volume of the mixture: V_J = (?V/?n_J)_p,T,n?.
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1. The partial molar volume is the
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V = n_AV_A + n_BV_B.
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1. The total volume of a mixture is
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?_ J = (?G/?n_J) _p,T,n?.
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2. The chemical potential can be defined in terms of the partial molar Gibbs energy,
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G = n_A?_A + n_B?_B.
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2. The total Gibbs energy of a mixture is
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dG = Vdp ? SdT + ?_Adn_A + ?_Bdn_B + · · ·.
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3. The fundamental equation of chemical thermodynamics relates the change in Gibbs energy to changes in pressure, temperature, and composition:
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?n_Jd?_J = 0.
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4. The Gibbs-Duhem equation is
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? = ?*+ RT ln(p/p*), where ?* is the standard chemical potential, the chemical potential of the pure gas at 1 bar.
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5. The chemical potential of a perfect gas is
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?_mixG = nRT(x_A ln x_A + x_B ln x_B).
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6. The Gibbs energy of mixing of two perfect gases is given by
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?_mixS = -nR(x_A ln x_A + x_B ln x_B).
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7. The entropy of mixing of two perfect gases is given by
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?_mixH = 0 for perfect gases.
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8. The enthalpy of mixing for perfect gases is
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(p_A = x_Ap_A*) throughout the composition range.
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9. An ideal solution is a solution in which all components obeys Raoult's law
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?_A = ?_A* + RT ln x_A.
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10. The chemical potential of a component of an ideal solution is given by
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(p_B = x_BK_B*) and the solvent obeys Raoult's law.
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11. An ideal-dilute solution is a solution for which the solute obeys Henry's law
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?_mixG = nRT(x_A ln x_A + xB ln xB).
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12. The Gibbs energy of mixing of two liquids that form an ideal solution is given by
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?_mixS = -nR(xA ln xA + xB ln xB).
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13. The entropy of mixing of two liquids that form an ideal solution is given by
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difference between the observed thermodynamic function of mixing and the function for an ideal solution.
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14. An excess function (XE) is the
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depends only on the number of solute particles present, not their identity.
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16. A colligative property is a property that
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?T = K_bb, where Kb is the ebullioscopic constant.
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17. The elevation of boiling point is given by
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?T = K_fb, where Kf is the cryoscopic constant.
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17. The depression of freezing point is given by
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a_A = p_A/p_A*.
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21. The activity is defined as
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?_A = ?_A* + RT ln a_A. The activity may be written in terms of the activity coefficient ?_A = a_A/x_A.
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22. The solvent activity is related to its chemical potential by
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Coulombic interactions between ions are dominant; a key idea of the theory is that of an ionic atmosphere.
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26. The Debye-Hückel theory of activity coefficients of electrolyte solutions is based on the assumption that
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detecting phase transitions that takes advantage of the effect of the enthalpy change during a first-order transition.
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5. Thermal analysis is a technique for
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p = p*_B + (p*_A ? p*_B)x_A.
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6. The vapour pressure of an ideal solution is given by
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y_A = x_Ap*_A/{p*_B + (p*_A ? p*_B)x_A}, y_B = 1 ? yA.
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6. The composition of the vapour of an ideal solution,
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p = p_A * p*_B/{p*_A + (p*_B ? p*_A)y_A}.
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7. The total vapour pressure of a mixture is given by
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constant composition in a phase diagram. A tie line is a line joining two points representing phases in equilibrium.
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8. An isopleth is a line of
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n?l? = n?l?.
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9. The lever rule allows for the calculation of the relative amounts of two phases in equilibrium:
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composition of the phases that are in equilibrium at various temperatures.
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10. A temperature-composition diagram is a phase diagram in which the boundaries show the
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boils without change of composition.
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11. An azeotrope is a mixture that
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do not mix in all proportions at all temperatures.
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12. Partially miscible liquids are liquids that
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highest temperature at which phase separation occurs in a binary liquid mixture.
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13. The upper critical solution temperature is the
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temperature below which the components of a binary mixture mix in all proportions and above which they form two phases.
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13. The lower critical solution temperature is the
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lowest melting point; a liquid with the eutectic composition freezes at a single temperature. A eutectic halt is a delay in cooling while the eutectic freezes.
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14. A eutectic is the mixture with the
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melts into its components and does not itself form a liquid phase.
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15. Incongruent melting occurs when a compound
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when the extent of reaction changes by a finite amount ??, the amount of A present changes from n_A,0 to n_A,0? ??.
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1. The extent of reaction (?) is defined such that,
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?_rG = (?G/??) _p,T; at equilibrium, ?_rG = 0.
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2. The reaction Gibbs energy is the slope of the graph of the Gibbs energy plotted against the extent of reaction:
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?_rG 0.
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3. An exergonic reaction is a reaction for which
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?_rG = ?_rG* + RT ln Q.
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4. The general expression for ?rG at an arbitrary stage of the reaction is
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?_rG* = ?RT ln K.
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5. The equilibrium constant (K) may be written in terms of ?_rG* as
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?rG*=?Products ??fG* ??Reactants ??fG*=??_J?_fG* (J).
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6. The standard reaction Gibbs energy may be calculated from standard Gibbs energies of formation,
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K = ?a_J ?_J Equilibrium .
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7. Thermodynamic equilibrium constant is an equilibrium constant K expressed in terms of activities (or fugacities):
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equilibrium constant.
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8. A catalyst does not affect the
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(?K/?p) _T = 0. However, partial pressures and concentrations can change in response to a change in pressure.
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9. Changes in pressure do not affect the equilibrium constant:
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responds in a way that tends to minimize the effect of the disturbance.
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10. Le Chatelier's principle states that a system at equilibrium, when subjected to a disturbance,
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Reactants and Products.
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11. Increased temperature favors the ____ in exothermic reactions and the _____ in endothermic reactions.
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d(ln K/dT) = ?_rH*/RT^2. To calculate K at one temperature in terms of its value at another temperature, and provided ?rH* is independent of temperature, we use ln K2 ? ln K1 = ?(?_rH*/R)(1/T_2 ? 1/T_1).
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12. The temperature dependence of the equilibrium constant is given by the van 't Hoff equation:
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produces electricity as a result of the spontaneous reaction occurring inside it.
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13. A galvanic cell is an electrochemical cell that
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non-spontaneous reaction is driven by an external source of current.
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13. An electrolytic cell is an electrochemical cell in which a
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removal of electrons from a species.
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14. Oxidation is the
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addition of electrons to a species
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14. Reduction is the
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electrons from one species to another.
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14. A redox reaction is a reaction in which there is a transfer of
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oxidation occurs.
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15. The anode is the electrode at which
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reduction occurs.
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15. The cathode is the electrode at which
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it is balanced by an exactly opposing source of potential so that the cell reaction occurs reversibly, the composition is constant, and no current flows.
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16. The electromotive force (emf) is the cell potential when
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??FE = ?_rG.
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17. The cell potential and the reaction Gibbs energy are related by
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E® = ?_rG® /?F.
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18. The standard emf is the standard reaction Gibbs energy expressed as a potential:
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E = E® ? (RT/?F) ln Q.
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19. The Nernst equation is the equation for the emf of a cell in terms of the composition:
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ln K = ?FE® /RT.
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20. The equilibrium constant for a cell reaction is related to the standard emf by
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Right-hand electrode and Left-hand electrode.
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21. The standard potential of a couple (E®) is the standard emf of a cell in which a couple forms the ______ and the standard hydrogen electrode is the _____.
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E® = E® (right) ? E® (left).
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22. To calculate the standard emf, form the difference of electrode potentials:
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dE® /dT = ?_rS® /?F.
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23. The temperature coefficient of cell potential is given by
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?_rS ® = ?FdE® /dT, ?_rH® = ??(FE ® ? TdE® /dT).
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24. The standard reaction entropy and enthalpy are calculated from the temperature dependence of the standard emf by:
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Method of determining heat change in a system by measuring heat exchanged in the surroundings
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Calorimetry
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Negative
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What enthalpy sign do exothermic reactions have?
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Positive
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What enthalpy sign do endothermic reactions have?
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States that if an equilibrium system is subject to change, the equilibrium shifts in the direction which tends to counter that change
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Le Châtelier's Principle
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Constant P
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Isobaric
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Constant T
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Isothermal
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Constant V
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Isochoric
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No heat flows in or out of the system (Q =0; ?U = W)
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Adiabadic
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?U = Q + W
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Relationship between heat and work
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W = -Pext (Vf - Vi)
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Work Equation
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H = U + PV
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Enthalpy
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?H = ?U + P?V
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Change in enthalpy at constant presssure
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Cv = (3/2)R
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Equation for Cv for monoatomic gas
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Cp = (5/2)R
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Equation for Cp for monoatomic gas
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Cv = (5/2)R
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Equation for Cv for diatomic gas
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Cp = (7/2)R
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Equation for Cp for diatomic gas
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f = c - p + 2 (f is the number of degrees of freedom of a system; c is the number of components is the system; p is the number of phases present)
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Gibb's phase rule
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At constant T and for a given sample of gas, the pressure of a gas is inversely proportional to its volume
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Boyle's Law
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, P?1/V
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Boyle's Law
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The volume of a given sample of gas at constant pressure is proportional to its absolute temperature
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Charles' Law
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Charles' Law
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V?T
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1) Gas consists of molecules in ceaseless random motion moving in straight linesbetween collisions , 2) The size of the molecule is negligible , 3) The molecules do not interact with each other or the wall of the vessel
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The Kinetic Model of Gases is based on what assumptions?
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c=?(3RT/M), Molar mass must be in kg mol-1, Temperature must be in K, Units = ms-1
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Root-mean-square (r.m.s) speed
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(p+a(n/v)^2)(V-nb) = RT , a and b are van der Waals parameters, specific for a given gas but independent of temperature
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What is the van der Waals equation of state?
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q = Cm x n x ?T , Units: J K-1 mol-1
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What is the equation for the molar heat capacity and give its units?
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, q = Cs x m x ?T , Units: J K-1 g-1 , The specific heat capacity of liquid water is 4.18 JK-1 g-1 Calculate the energy required to heat 1 mol of water from 25 °C to 90 °C , q = Cs x n x ?T = 4.18 x 18 x (90-25) = 4.9kJmol-1
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What is the equation for the specific heat capacity and give its units?
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Work done = external pressure x change in volume, The system is losing energy the external pressure is negative
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When a gas expands and moves a piston, how do you calculate the work done ?
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Both extensive and a state function
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What type of property is internal energy?
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Internal energy is the total energy of a system, It has the symbol U, ?U = q + w
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What is internal energy, give its symbol and give the equation for a change in internal energy
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?U = ?H -p?V p is pressure (constant)
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What is the relationship between enthalpy change and internal energy?
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?S = q(rev) / T , q(rev) = quantity of heat added reversibly ?S = Cp ln (Tf/Ti)
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What is the equation for the variation of entropy with temperature?
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K is the thermodynamic equilibrium constant and is calculated at equilibrium whereas Q although calculated in the same way it doesn't have to be at equilibrium
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What is the difference between K and Q?
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Q ; K
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What relationship between Q and K has a tendency to form products?
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Q ; K
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What relationship between Q and K has a tendency to form reactants?
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?rG = -RT lnK
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What is the relationship between ?rG and K?
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lnK = (?rS/R) - (?rH/RT)
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What is the van't Hoff equation for a reaction at a given temperature
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ln(K2/K1) = - ?rH/R(1/T2 - 1/T1) , ANS = 6.7 x 10-2 at 1200K
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The equilibrium for the dissociation of one mole of iodine vapour is 3.94 x10-4 at 900K and the standard enthalpy is 154 kJmol-. Calculate the equilibrium constant at 1200K assuming the standard enthalpy remains constant
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True
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At low vapour pressure, it is easy for a liquid to transition into a gas, true or false?
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Zn(s) | Zn2+(aq) || Cu2+(aq) | Cu(s)
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What is a Daniell cell's cell diagram?
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An electrochemical cell that produces electricity as a result of a spontaneous reaction
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What is a Galvanic Cell?
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A non-spontaneous reaction is forced by an external source of current
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What is an Electrolytic Cell?
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Galvanic cells in which the reagents are supplied continuously
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What is a Fuel Cell?
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Left
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During cell notation where is the oxidation half reaction?
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Right
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During cell notation where is the reduction half reaction?
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Left
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What side does the anode appear in the cell notation?
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Right
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What side does the cathode appear in the cell notation?
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Hg(l) | Hg2Cl2(s) | Cl-(aq)
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What is the cell notation for a calomel electrode?
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reduction
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Standard electrode potentials are given as? (oxidation/reduction)
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?rG = we = -VQ, 1J = 1V x 1C
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What is the relationship between electrical work and standard gibbs energy change for a reaction?
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?rG will be negative therefore the reaction is spontaneous
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If Ecell is positive what will ?rG be?
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E = hv = hc/ ? , Units: Joules
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What is the energy per photon and what is its units?
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T = It/I0 , light intensity emmitted / light intensity added
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What is the equation for transmittance?
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A = - log T
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What is the equation for absorbance?
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T = 0.8 , A= - log (0.8) = 0.1
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If a sample absorbs 20% of light what is T and A?
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A = ?cl , A has no units so the units must cancel out , ? usually in dm3 mol-1 cm-1 , c has to be in mol dm-3 , l has to be in cm
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What is Beer-Lambert Law? Give units
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Force exist between the molecules of gasses when Z;1
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Repulsive
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Governs the temperature dependence of pressure in a two-phase, one component system
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Clapeyron equation
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Gives the relationship between pressure and temperature for a two phase, one component system assuming that the vapor phase is ideal and the molar volume of the condensed phase is negligible compared to vapor phase
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Clausius-Clapeyron equation
