Gamsat Physical Chemistry – Flashcards
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What is the triple point on a phase diagram?
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The point at which solid, liquid and gas coexist
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What is the critical temperature on a phase diagram?
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Is the temperature of a substance at which it cannot exist as a liquid
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What is the critical pressure on a phase diagram?
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It is the minimum pressure at which liquefication can take place at the critical temperature
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Why does ice float?
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Water expands as it freezes
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What is the impact of increasing pressure on the melting point of water?
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Decreases the melting point
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What is the impact of increasing pressure of boiling point?
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Increases the temperature
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What is the impact of increasing pressure on ice's melting point?
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Lowers the melting point
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What is the impact of increasing pressure on the boiling point of water?
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Increases the boiling point
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What is the impact of increasing pressure on a substance with a positive slope on a phase diagram?
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It will increase both the boiling point and the melting point
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What kind of equilibrium is a saturated solution in?
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The dissolved and undissolved solute are in dynamic equilibrium
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What is Henry's Law?
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At constant temperature, the solubility of a gas in a liquid is proportional to its partial pressure above a liquid. If pressure is applied to a gas in dynamic equilibrium with a liquid, more gas will dissolve.
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What are the four colligative properties?
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Vapour pressure Boiling point Melting point Osmotic pressure
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What happens to a solute that is not ionic in a solvent?
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When 1 mole of solute is dissolved, 1 mole of solute particles occur in the solution
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What is Raoult's Law?
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The vapour pressure of a solvent in a solution of a non-volatile solute is directly proportional to the mole fraction of the solvent in the solution.
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How do you find the boiling point elevation of temperature?
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Change in boiling point= molaity boiling point constant x molaity of solution x Van't Hoff factor
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How do you find the freezing point depression of temperature?
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Change in freezing point = solvent constant x molaity x Van't Hoff factor
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What does osmotic pressure depend on?
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The number of, not the kind of solute particles in solution.
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How do you find osmotic pressure?
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Osmotic pressure = constant x gas constant x temperature (kelvin) x molarity
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What is distillation?
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A mother that heats and cools a liquid in order to separate the mixture of liquids
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What is surface tension?
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The tension on the surface of a liquid caused by intermolecular forces
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What is a colloid?
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A mixture in which one substance of microscopically dispersed insoluble particles is suspended throughout another substance
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What is the rate of reaction?
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The change in a substance's concentration divided by the time it takes for that change to occur.
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What is the rate-determining step?
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The instantaneous reaction rate is the tangent to the curve of the graph of molar concentration versus time.
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What does k represent?
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The rate constant
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What does k depend on?
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The reaction itself and the temperature
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What is the rate law?
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It is experimentally determined and depends on the rate-determining step
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The overall order of a reaction is a+b+c+...... The first order reaction is?
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rate= k.[A]
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The overall order of a reaction is a+b+c+...... The second order reaction is?
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rate= k.[A]^2 or k.[A].[B] or k[B]^2
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The overall order of a reaction is a+b+c+...... The zeroth order reaction is?
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rate=k and is independent of the concentrations of the reactants
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What is the general formula that shows how k varies with temperature?
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k= A/e^(Ea/{RT}) or k= In A-E(a)/{RT}
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What is the frequency factor?
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Represents the frequency of collision of molecules.q
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What does Ea represent?
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The activation energy barrier. This is the energy that must be available when particles collide, for the reaction to take place.
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What are catalysts?
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Provide alternative paths with lower activation energies but are not consumed in the process.
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What do catalysts do to the bonds in the reactant molecule?
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It weakens the bonds in the reactant molecule that is bound to the catalyst.
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Where on the catalyst is the substrate bound?
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Active site
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What is the impact of the catalyst on the activation energy of a reaction?
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Lowers the activation energy
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What is dynamic equilibrium?
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It is reached when the rates in both forward and reverse reactions are equal.
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What is the equilibrium constant?
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Keq=[C]^c[D]^d/[A]^a[B]^b Is the ratio of the forward and backward rate constants
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Are solids added in equilibrium constants?
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No
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What does Q represent?
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The reaction quotient. This is the ratio of concentrations of products to those of reactants
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What is Le Chatelier's principle?
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When a stress is applied to a system in dynamic equilibrium, the equilibrium adjusts to minimise the effect of the stress
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When a system is at Q<Keq?
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The reaction proceeds dominantly to the right
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When a system is at Q>Keq?
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The reaction proceeds dominantly to the left
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According to Le Chatelier's Principle what would happen when the temperature increases for an exothermic reaction?
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Will force the reaction towards the left.
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According to Le Chatelier's Principle what would happen when the temperature decreases for an exothermic reaction?
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Will force the reaction towards the right.
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According to Le Chatelier's Principle what would happen when the temperature increases for an endothermic reaction?
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Will force the reaction to the right
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According to Le Chatelier's Principle what would happen when the temperature decreases for an endothermic reaction?
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Will force the reaction to the left
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What happens when a reasonably insoluble solid is added to water?
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Some of the solid will dissolve and become ions and an equilibrium is established between the undissolved solid and the ions
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What does Ksp represent?
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The solubility product
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What does Ks represent?
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The solubility contant eg) AgCl Ks= [Ag+][Cl-]
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What is the first law of thermodynamics?
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Where an isolated system is defined as one that can do no work on anything else and is insulated from the transfers of energy as heat, the internal energy of an isolated system is constant
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The change in enthalpy deltaH of a reacting system is.....
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Equal to the heat released or absorbed at constant pressure.
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When deltaH is positive?
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It is an endothermic reaction
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When deltaH is negative?
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It is an exothermic reaction
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Enthalpy increases when a substance changes state from?
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Solid-> liquid Liquid->Gas
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Enthalpy decreases when a substance changes state from?
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Gas-> Liquid Liquid-> Solid
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What does the enthalpy system depend on?
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Its mass, volume, temperature, pressure and physical phase but it is not dependent on the process of achieving these properties
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What is Hess's Law?
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A reaction enthalpy is the sum of the enthalpies of any series of reactions into which the overall reaction may be divided
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What is entrophy change?
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The change in molecular disorder caused by the reaction
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What is the standard reaction entropy for any reaction?
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Is the difference in entropy between the products in their standard states and the entropy of the reactants in their standard states
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When deltaS is negative?
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The reaction leads to less disorder
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When deltaS is positive?
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The reaction leads to more disorder
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What is the second law of thermodynamics?
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A spontaneous change is accompanied by an increase in the total energy of the system and its surroundings
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How do you calculate Gibbs free energy?
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deltaG=deltaH-TdeltaS
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If deltaH is negative?
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The reaction is spontaneous
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If deltaH is positive?
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The reaction is non-spontaneous
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What does it mean when something is thermodynamically unstable?
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When the energy level of products is lower than that of reactants
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If deltaG is negative and the reaction is spontaneous, when will the products be favoured at equilibrium?
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When K>1
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If deltaG is positive and the reaction is not spontaneous, when will the reactants be favoured at equilibrium?
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When 0<K<1
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What is a bronsted acid (HA)?
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A proton donor
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What is a bronsted base (B)?
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A proton acceptor
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What does Ka stand for?
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The acid ionisation constant Ka=[H3O+][A-]/[HA]
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What does Kb stand for?
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The base ionisation constant Kb= [HB+][OH-]/[B]
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pH is defined as?
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-log[H3O+]
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pOH is defined as?
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-log[OH-]
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pKa is defined as?
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-logKa
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pKb is defined as?
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-logKb
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Is water a bronsted acid or base?
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Water can act as either a bronsted acid or base
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In aqueous solutions (at 25degreesC) Kw is?
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Kw= [H3O+][OH-]=10^-14
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pKw is defined as?
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pKa=pH + pOH = 14
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What defines a strong acid/base?
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One that ionises almost completely in water
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What is an equivalence point?
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When the moles of the titrant is equal to the moles of the unknown solution
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For a strong acid
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Ka is higher and pKa is lower
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For a weak acid
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Ka is lover and pKa is higher
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For a strong base
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Kb is higher and pKb is lower
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For a weak base
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Kb is lower and pKb is higher
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What is a buffer solution?
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A solution that resists change in pH when small amounts of acid or base are added.
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An acid buffer solution is made up of
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A weak acid with a common ion of its conjugate strong base
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A base buffer solution is made up of
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A weak base with the common ion of its conjugate acid
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What is the common ion in HA and A-
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A-
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Is a buffered acid solution less or more acidic than the weak acid solution alone?
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Less acidic
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The pH of a buffer solution is given by
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pH= pKa+log[conjugate base/acid]
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The pOh of a buffer solution is given by
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pOH= pKb +log[conjugate acid/base]
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When the [conjugate base] = [acid], the buffer solution is at its most effective. At this point.....
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log10[conjugate base]/[acid] = log10(1) = 0 and pH= pKa
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What is the henderson hasselbalch equation for pH?
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ph=pKa + log[moles of bases added initially]/[mole of acid added initially]
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What is the henderson hasselbalch equation for pOH?
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pOH = pKb + log[moles of acid added initially]/[moles of base added initially]
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When do acid buffer solutions work best?
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At pH levels on the titration curve of weak acid-strong base where the curve is flattest.
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What are polyprotic bases?
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They can accept more than one proton
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What are polyprotic acids?
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They can donate more than one proton
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What are zwitterions?
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Compounds that have a positive charge on one atom and a negative charge on another atom.
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What is the buffer capacity of a solution?
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The amount of H3O+ or OH- ions that that need to be added to the solution to change its pH by 1.
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If hydrogen is attached to a very electronegative elements, what happens to the hydrogen?
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The hydrogen will be more acidic
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Write the order of least acidic to most acidic: Phenols, Alcohols and Carboxylic Acids
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Alcohols, Phenols, Carboxylic Acids
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What is the name of the carbon next to any functional group?
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α (alpha) carbon
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What is the name of any protons attached to the α-carbon?
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α-protons or α-hydrogens
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What is oxidation?
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Electron loss
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What is reduction?
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Electron gain
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What occurs in a redox reaction?
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Oxidation and reduction
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How do you calculate the oxidation state of each atom in a molecule?
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oxidation state= number of valence electrons - number of assigned electrons
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In organic chemistry oxidation results in?
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Increases the oxygen, nitrogen or halogen content of a molecule or decreases the hydrogen content
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In organic chemistry reduction results in?
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Decreases the oxygen, nitrogen or halogen content of a molecule or increases the hydrogen content
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Name some oxidising agents
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Potassium Dichromate, Potassium Permanganate, Pyridinium chlorochromate, Ozone plus Zn/H2O
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Name some reducing agents
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LiAlH4, NaBH4, H2 with a palladium or nickel catalyst, Na or Li/NH3, Zn/HCl
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Where does oxidation occur in the electrode?
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Anode
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Where does reduction occur in the electrode?
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Cathode
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What are cations and their relation to an electrode?
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Cations are positively charged and flow towards the cathode
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What are anions and their relation to an electrode?
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Anions are negatively charged and flow towards the anode.
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What do galvanic cells produce?
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Electricity
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How do you find the voltage produced?
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Is equal to the difference in the standard reduction potential between the cathode and the anode
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What is Faraday's law of electrolysis?
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The amount(in moles) of product formed by an electric current during electrolysis is directly proportional to the amount (in moles) of electrons used in the process.
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What is electrolytic corrosion?
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Occurs when two metals with reasonably different values come in contact through an electrolyte.
