Physical Chemistry I Final Review – Flashcards
103 test answers
Unlock all answers in this set
Unlock answers 103question
the value of the property changes with the amount of the material that is present; ex. mass, internal energy
answer
extensive property
Unlock the answer
question
independent of amount of material present; ex. temp or density
answer
intensive property
Unlock the answer
question
the value of a particular property only depends on the state of the system at that time
answer
state functions
Unlock the answer
question
volume, pressure, internal energy and entropy
answer
examples of state functions
Unlock the answer
question
property that depends upon the path by which a system in one state is changed to another state
answer
path function
Unlock the answer
question
heat and work
answer
ex. of path functions
Unlock the answer
question
no account of how the state was prepared is necessary
answer
When performing calculations on state functions
Unlock the answer
question
the total energy of an isolated thermodynamic system is constant; conservation of energy
answer
The first law of thermodynamics
Unlock the answer
question
energy cannot be created or destroyed
answer
conservation of energy
Unlock the answer
question
∆U = q + w
answer
first law equation
Unlock the answer
question
energy is gained by the system as heat or work
answer
U, q, and w are positive if
Unlock the answer
question
energy is lost b the energy as heat or work
answer
U, q, and w are negative if
Unlock the answer
question
path; they do not depend on the initial and final states but on how the final state is reached
answer
heat and work are ___ functions
Unlock the answer
question
w=-Pex∆V, U=-Pex∆V + q
answer
When there is pV/expansion work, w= _____, U= _____
Unlock the answer
question
∆V=0, and ∆U=q
answer
if a reaction takes place in a sealed container at fixed volume then,
Unlock the answer
question
robust metal container in which a reaction takes place. As the reaction exchanges heat with the surroundings, the temperature of the surroundings changes. ∆U=q. temperature rise is related to the heat output form the reaction; temperature of a system is proportional to the amount of heat input into it by the heat capacity, C=dq=CdT
answer
bomb calorimeter
Unlock the answer
question
relates the amount of temperature of a system to the amount of heat which is input into the system
answer
heat capacity
Unlock the answer
question
Cp= Cv + nR
answer
Cp and Cv are the same for solids and liquids, but For gases
Unlock the answer
question
constant volume heat capacity
answer
Cv
Unlock the answer
question
constant pressure heat capacity
answer
Cp
Unlock the answer
question
dU = CvdT or ∆U =Cv∆T, when Cv is independent of temperature
answer
At constant volume, the heat supplied is equal to the change in internal energy, so it is possible to write
Unlock the answer
question
molar heat capacity
answer
Cm
Unlock the answer
question
H= U + pV
answer
enthalpy equation
Unlock the answer
question
constant pressure
answer
The enthalpy change for a process is equal to the heat exchange at
Unlock the answer
question
∆H=∆U+ p∆V (note: this is equal to Q)
answer
Enthalpy equation at constant pressure is
Unlock the answer
question
∆H=∆U+ ∆nRT, where ∆n is the molar change in gaseous component
answer
For a chemical system which releases or absorbs a gas a constant pressure, the enthalpy change is related to internal energy by
Unlock the answer
question
enthalpy increases
answer
endothermic
Unlock the answer
question
enthalpy decreases
answer
exothermic
Unlock the answer
question
∆H=Cp∆T, provided that Cp does not appreciably change over the temperature range of interest. Otherwise, ∆H=∫CpdT.
answer
enthalpy change arising from a temperature change at constant pressure is
Unlock the answer
question
∆H=∆H(products) - ∆H(reactants)
answer
In a chemical reaction, the enthalpy change is equal to the difference between the reactants and products
Unlock the answer
question
∆H2 - ∆H1 =∫∆CpdT
answer
Where Cp does not appreciably change over the temperature range of interest, enthalpy may be expressed as
Unlock the answer
question
∆H=q
answer
When the only work done by the system is pV work, at constant pressure
Unlock the answer
question
the interanl energy change of that system and the work done by the system in expanding against the constant external pressure
answer
heat exchanged by a system at constant pressure is equal to the sum of the
Unlock the answer
question
true
answer
an increase in enthalpy leads to an increase in its temperature (true or false)
Unlock the answer
question
exothermic process
answer
Loss of heat from a system lowers its temperature and is referred to as an
Unlock the answer
question
independent of the process from which they were formed
answer
Because enthalpy is a state function, the absolute enthalpy associated with the reactants and products in a reaction are
Unlock the answer
question
the overall enthalpy change for a reaction is equal to the sum of the enthalpy changes for the individual steps in the reaction measured at the same temperature
answer
Hess's Law
Unlock the answer
question
reverse the direction of the transfer through an infinitesimal change in the conditions
answer
if energy is transferred reversibly to or from a system, it must be possible to
Unlock the answer
question
dq(rev)/T
answer
for a reversible process at constant temperature, the change in entropy, dS, is given by
Unlock the answer
question
dS>dq/T
answer
For an irreversible process,
Unlock the answer
question
the entropy of a perfectly crystalline solid at the absolute zero of temperature is zero
answer
the third law of thermodynamics
Unlock the answer
question
reversibly or irreversibly
answer
any process involving the transfer of energy from one body to another may take place
Unlock the answer
question
energy is transferred in such a way that at any point in the process the transfer may be reversed by an infinitesimally small change in the conditions. The system is therefore in equilibrium throughout the transfer. This means that the energy must be transferred infinitely slowly.
answer
reversible process
Unlock the answer
question
energy is transferred in a manner which results in random motion and some of the energy is dissipated as heat. The process is irreversible because a proportion of this heat is dispersed irrecoverably, and the original conditions cannot be generated without work being done on the system.
answer
irreversible process
Unlock the answer
question
less
answer
in isothermal expansion of an ideal gas against an external pressure, the amount of work done in a reversible process is ____ than the amount of work done for an irreversible process
Unlock the answer
question
property and state function
answer
entropy is a thermodynamic ____ of a system and a ___ function
Unlock the answer
question
dS=dq(rev)/T (reversible process), dS/T(irreversible process)
answer
For any process in any system, under isothermal conditions, the change in entropy, dS, is defined as:
Unlock the answer
question
they are the same because entropy is a state function
answer
How does the system entropy change for a irreversible process relate to that of a reversible process
Unlock the answer
question
-dq/dT
answer
the entropy change of the surroundings is
Unlock the answer
question
zero
answer
the total entropy change for a reversible process is
Unlock the answer
question
greater than zero
answer
the total entropy change for an irreversible process is
Unlock the answer
question
dq(rev)=CdT and dS=CdT/T, ∆S=∫(C/T)dT
answer
If heat is added reversibly to a system, it is possible to measure the system entropy changes by measuring the heat capacity. Show the logic here.
Unlock the answer
question
q=∆H(phase change) and ∆S=∆H(phase change)/T
answer
For a phase change at constant pressure, what are q and ∆S?
Unlock the answer
question
∆S(vap) is approximately equal to 85 J/K mol for most materials. (Svap is noted for having a large absolute entropy of the gas phase)
answer
Trouton's Rule
Unlock the answer
question
zero
answer
the entropy of a perfectly crystalline solid at absolute temperature of zero is
Unlock the answer
question
has a measurable absolute value for any system
answer
because it is possible to measure entropy changes from a reference point using heat capacity measurements, entropy (unlike enthalpy and internal energy)
Unlock the answer
question
has a natural tendency to occur without the need for input of work into the system
answer
spontaneous process
Unlock the answer
question
expansion of a gas in a vacuum, ball rolling down a hill, flow of heat from a hot body to a cold one
answer
spontaneous process examples
Unlock the answer
question
energy in the form of work must be put into the system
answer
for a nonspontaneous process to occur
Unlock the answer
question
compression of a gas into a smaller volume, the raising of a weight against gravity, the flow of heat from a cold body to a hotter one
answer
examples of non-spontaneous processes
Unlock the answer
question
increases for an irreversible process and remains constant for a reversible process
answer
For entropy of an isolated system ___ for a irreversible process and ______ for a reversible process
Unlock the answer
question
decreases
answer
the entropy of an isolated system never
Unlock the answer
question
the standard entropies of the initial and final states of the system
answer
Because entropy is a state function, entropy changes in a system may be calculated from
Unlock the answer
question
quickly or randomly; it can take an infinite amount of time to occur
answer
Spontaneous does not mean that the reaction occurs
Unlock the answer
question
work
answer
a spontaneous process may be harnessed to do ____ on another system
Unlock the answer
question
does not have a natural tendency to occur
answer
non-spontaneous process
Unlock the answer
question
non-spontaneous
answer
in any system, the reverse of a spontaneous process must be
Unlock the answer
question
sum of the entropy change of the system and in the surroundings, and it must be greater than or equal to zero to comply with the second law
answer
the total entropy change is the
Unlock the answer
question
The total entropy change is greater than zero. For example, the reaction can be exothermic and the heat lost to the surroundings causes the ∆S of the surroundings to be positive and greater than the ∆S of the system.
answer
How can the entropy change of the system be less than 0, but the reaction still spontaneous.
Unlock the answer
question
G=H-TS
answer
Gibbs Free energy equation
Unlock the answer
question
∆G=∆H-T∆S
answer
at constant temperature and pressure, finite changes in free energy may be expressed as
Unlock the answer
question
volume
answer
The Helmholtz free energy, A, is applied at constant
Unlock the answer
question
A=U-TS
answer
The Helmholtz free energy equation
Unlock the answer
question
at constant temperature and pressure
answer
When are Gibbs free energy is equal to -T∆S
Unlock the answer
question
at constant temperature and volume
answer
Helmholtz free energy is equal to -T∆S
Unlock the answer
question
∆G<0 (constant pressure) and ∆A<0 (constant volume)
answer
For a spontaneous process what are Gibbs and Helmholtz free energy values?
Unlock the answer
question
state functions without measurable absolute values
answer
Gibbs and Helmholtz free energies are
Unlock the answer
question
the maximum amount of work, other than volume expansion work, which may be obtained from a process
answer
Define free energy change
Unlock the answer
question
spontaneous process
answer
∆G is negative for a
Unlock the answer
question
An exothermic reaction ∆H0
answer
What process is always spontaneous?
Unlock the answer
question
An exothermic reaction ∆H<0 with a negative entropy change ∆S<0
answer
What process is spontaneous only at low temperatures?
Unlock the answer
question
An endothermic reaction ∆H>0 with a positive entropy
answer
What process is spontaneous only at high temperatures?
Unlock the answer
question
T=∆H/∆S
answer
The temperature at which a reaction becomes spontaneous is
Unlock the answer
question
(d/dT(G/T))p = -H/T^2
answer
the Gibbs-Helmholtz equation relates the temperature dependence of gibbs free energy. It is expressed as
Unlock the answer
question
S(surroundings) = -∆H(system)/T
answer
∆S(surroundings) is related to the enthalpy change in the system at constant pressure through the relationship
Unlock the answer
question
∆S(total)= ∆S(surr) + ∆S(system) At constant pressure ∆S(total)= -∆H/T + ∆S(system) -T∆S(total)= ∆H(surr) -T∆S(system) ∆G= ∆H(surr)- T∆S(system)
answer
Derive Gibbs free energy equation from ∆S total
Unlock the answer
question
∆G=-T∆S(total)
answer
Gibbs free energy is the measure of the total entropy change for a process
Unlock the answer
question
spontaneous process at constant pressure
answer
Gibbs free energy is less than zero for a
Unlock the answer
question
spontaneous process at constant volume
answer
Helmholtz free energy is less than zero for a
Unlock the answer
question
∆G=∆G(standard) + RTln(Q), where Q is the reaction quotient
answer
Free energy varies markedly with composistion by the expression
Unlock the answer
question
∆S(total)= ∆S(surr) + ∆S(system)
answer
Derive Helmholtz free energy from total entropy
Unlock the answer
question
for closed system where changes occur under constant volume conditions, such as reactions or processes in solids
answer
When is helmholtz free energy useful
Unlock the answer
question
most process take place at constant pressure
answer
Why is the gibbs free energy more commonly used than helmholtz free energy
Unlock the answer
question
represents the maximum amount of work, other than pV work, which may be obtained from a process
answer
The most important property of the free energy is that it not only provides an indicaton of the spontaneity of a process but it also
Unlock the answer
question
some heat from the system must be lost to the surroundings to contribute to ∆S(surroundings) such that the total entropy is greater than zero
answer
In the case of a reaction for which ∆Ssystem is negative, what must happen for the reaction to be spontaneous
Unlock the answer
question
when the rate of the forward and backward reactions are equal
answer
When is equilibrium established
Unlock the answer
question
...
answer
at equilibrium, the gibbs free energy changes for both the forward and backward reactions are zero
Unlock the answer
question
∆G=∆G(standard) + RTln(K), where K is the equilibrium constant
answer
what is gibbs free energy in terms of the equilibrium constant
Unlock the answer
question
property that depends only on the number of solute molecules present
answer
colligative property
Unlock the answer
