PHYSICAL CHEMISTRY FINAL EXAM REVISION PROBLEMS 2024/2025. THE
LATEST REVISION QUESTIONS AND CORRECT ANSWERS IN 2024/2025.
(ALREADY GRADED A+) (LATEST 2024 UPDATE)
Draw a Carnot cycle diagram and describe the event occurring at each step - ANSWER- I)
Reversible Isothermal Expansion
II) Reversible Adiabatic Expansion
III) Reversible Isothermal Compression
IV) Reversible Adiabatic Compression
The boiling point of water at a pressure of 50 atm is 538 K. Compare the theoretical efficiencies
of a steam engine operating between:
1) The boiling point of water at 1 atm
2) 50 atm, assuming the temperature of the sink to be 308 K - ANSWER- 1) P(1)=1 atm
T(C)=308 K
T(H)=373 K
η=1-(T(C)/T(H))
η=17%
2) P=50 atm
T(C)=308 K
T(H)=538 K
η=1-(T(C)/T(H))
,η=43%
The temperature of 20 L N(2) at 5.00 kPa is increased from 293 K to 673 K at constant volume.
Calculate the change in entropy. Assume ideal behavior - ANSWER- V=0.02 m^3
T(1)=293 K
T(2)=673 K
P=5000 Pa
C(V)=20.8 (Diatomic)
n=PV/RT
ΔS=nC(V)ln(T(2)/T(1))
n= 0.041 mol
ΔS=0.71 J/K
If 1.00 mol N(2) gas expands isothermally from 22.0 L to 44.0 L. What is the entropy change?
Assume ideal behavior. - ANSWER- n=1 mol
V(1)=22.0 L
V(2)=44.0 L
ΔS=nRln(V(2)/V(1))
ΔS=5.76 J/K
Calculate the change in entropy when 1 mol of a perfect gas expands isothermally to twice its
initial volume
1) Reversibly
, 2) Irreversibly - ANSWER- 1) n=1 mol
V(2)/V(1)=2
ΔS=nRln(V(2)/V(1))-nRln(V(2)/V(1))
ΔS= 0
2) n=1 mol
V(2)/V(1)=2
ΔS=nRln(V(2)/V(1))
ΔS=5.76 J/K
Determine the change in entropy when 1 mol of He at 298 K and 1.5 atm expands isothermally to
298 K and 15 atm, then expands isobarically to 100 K and 15 atm. - ANSWER- n=1 mol
C(P)=20.8
T(1)=298 K
T(2)= 100 K
P(1)=1.5 atm
P(2)=15 atm
ΔS=nC(P)ln(T(2)/T(1))+nRln(P(1)/P(2))
ΔS=-41.84 J/K
Calculate q, w, ΔU, ΔH, ΔS(system), and ΔS(universe) for 2 mol of a monoatomic ideal gas at 300
K and 5 L that expands adiabatically to 20 L at 250 K. - ANSWER- q=0
LATEST REVISION QUESTIONS AND CORRECT ANSWERS IN 2024/2025.
(ALREADY GRADED A+) (LATEST 2024 UPDATE)
Draw a Carnot cycle diagram and describe the event occurring at each step - ANSWER- I)
Reversible Isothermal Expansion
II) Reversible Adiabatic Expansion
III) Reversible Isothermal Compression
IV) Reversible Adiabatic Compression
The boiling point of water at a pressure of 50 atm is 538 K. Compare the theoretical efficiencies
of a steam engine operating between:
1) The boiling point of water at 1 atm
2) 50 atm, assuming the temperature of the sink to be 308 K - ANSWER- 1) P(1)=1 atm
T(C)=308 K
T(H)=373 K
η=1-(T(C)/T(H))
η=17%
2) P=50 atm
T(C)=308 K
T(H)=538 K
η=1-(T(C)/T(H))
,η=43%
The temperature of 20 L N(2) at 5.00 kPa is increased from 293 K to 673 K at constant volume.
Calculate the change in entropy. Assume ideal behavior - ANSWER- V=0.02 m^3
T(1)=293 K
T(2)=673 K
P=5000 Pa
C(V)=20.8 (Diatomic)
n=PV/RT
ΔS=nC(V)ln(T(2)/T(1))
n= 0.041 mol
ΔS=0.71 J/K
If 1.00 mol N(2) gas expands isothermally from 22.0 L to 44.0 L. What is the entropy change?
Assume ideal behavior. - ANSWER- n=1 mol
V(1)=22.0 L
V(2)=44.0 L
ΔS=nRln(V(2)/V(1))
ΔS=5.76 J/K
Calculate the change in entropy when 1 mol of a perfect gas expands isothermally to twice its
initial volume
1) Reversibly
, 2) Irreversibly - ANSWER- 1) n=1 mol
V(2)/V(1)=2
ΔS=nRln(V(2)/V(1))-nRln(V(2)/V(1))
ΔS= 0
2) n=1 mol
V(2)/V(1)=2
ΔS=nRln(V(2)/V(1))
ΔS=5.76 J/K
Determine the change in entropy when 1 mol of He at 298 K and 1.5 atm expands isothermally to
298 K and 15 atm, then expands isobarically to 100 K and 15 atm. - ANSWER- n=1 mol
C(P)=20.8
T(1)=298 K
T(2)= 100 K
P(1)=1.5 atm
P(2)=15 atm
ΔS=nC(P)ln(T(2)/T(1))+nRln(P(1)/P(2))
ΔS=-41.84 J/K
Calculate q, w, ΔU, ΔH, ΔS(system), and ΔS(universe) for 2 mol of a monoatomic ideal gas at 300
K and 5 L that expands adiabatically to 20 L at 250 K. - ANSWER- q=0
