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Exam 3 with Answer Key - Physical Chemistry | CHEM 341, Exams of Physical Chemistry

Material Type: Exam; Professor: Huang; Class: PHYSICAL CHEMISTRY; Subject: Chemistry; University: Jackson State University; Term: Fall 2007;

Typology: Exams

Pre 2010

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CHEM 341, Fall 2007 Name:___________________
Exam 3
The value of the gas constant R is 0.0820574 L atm mol-1 K-1, 1.98721 cal mol-1 K-1, and
8.31447 J mol-1 K-1. The atomic molar mass of H is 1.0079 g/mol; for C it is 12.01 g/mol;
for O it is 16.00 g/mol. 1 atm = 760 Torr; 1 dm3 = 1 L; 1 L = 1000 cm3; 1 m3 = 1000 L.
Answer all questions and show your working. Write clearly. No credit will be given for
illegible or ambiguous work.
A. Multiple choice (30 points)
1. _____ Given for aluminum that
T fusion = 933 K
fus H ° = 2538 cal mol-1
Cp,m (liquid) = 8.2 cal K-1 mol -1
Cp,m (solid) = 7.6 cal K-1 mol-1
Calculate the entropy change for aluminum when one mole of the metal is heated
from 873 K to 973 K.
A) 0.035 cal K-1 mol -1
B) 1.23 cal K-1 mol -1
C) 1.72 cal K-1 mol -1
D) 3.57 cal K-1 mol -1
E) -1.87 cal K-1 mol -1
2. _____ Consider the following reaction:
S2Cl2 (g) + 2 OCl2 (g) 2 SOCl2 (g) + Cl2 (g)
Δf G° (kJ/mol) -32 97.9 -320 0.0
Δr G° for the reaction in kJ/mol is:
A) -804
B) -476
C) -386
D) -413
E) -799
3. _____ The value of Δf G° for Mg (g) is 113.10 kJ mol-1 at 298.15 K, and Δf H° for Mg (g) is
147.70 kJ mol-1 at the same temperature. Assuming that ΔfH° is constant in the
interval 250-400 K, calculate Δf G° for Mg (g) at 250 K.
A) 105.58 kJ mol-1
B) 142.11 kJ mol-1
C) 70.98 kJ mol-1
D) 163.33 kJ mol-1
E) 118.69 kJ mol-1
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CHEM 341, Fall 2007 Name:___________________ Exam 3

The value of the gas constant R is 0.0820574 L atm mol-1^ K-1, 1.98721 cal mol-1^ K-1, and 8.31447 J mol-1^ K-1. The atomic molar mass of H is 1.0079 g/mol; for C it is 12.01 g/mol; for O it is 16.00 g/mol. 1 atm = 760 Torr; 1 dm^3 = 1 L; 1 L = 1000 cm^3 ; 1 m^3 = 1000 L. Answer all questions and show your working. Write clearly. No credit will be given for illegible or ambiguous work.

A. Multiple choice (30 points)

  1. _____ Given for aluminum that T (^) fusion = 933 K ∆fus H ° = 2538 cal mol- Cp,m (liquid) = 8.2 cal K-1^ mol - Cp,m (solid) = 7.6 cal K-1^ mol- Calculate the entropy change for aluminum when one mole of the metal is heated from 873 K to 973 K. A) 0.035 cal K-1^ mol - B) 1.23 cal K-1^ mol - C) 1.72 cal K-1^ mol - D) 3.57 cal K-1^ mol - E) -1.87 cal K-1^ mol -
  2. _____ Consider the following reaction: S 2 Cl 2 (g) + 2 OCl 2 (g) → 2 SOCl 2 (g) + Cl 2 (g) Δf G° (kJ/mol) -32 97.9 -320 0. Δr G° for the reaction in kJ/mol is: A) - B) - C) - D) - E) -
  3. _____ The value of Δf G° for Mg (g) is 113.10 kJ mol-1^ at 298.15 K, and Δf H° for Mg (g) is 147.70 kJ mol-1^ at the same temperature. Assuming that ΔfH° is constant in the interval 250-400 K, calculate Δf G° for Mg (g) at 250 K. A) 105.58 kJ mol- B) 142.11 kJ mol- C) 70.98 kJ mol- D) 163.33 kJ mol- E) 118.69 kJ mol-
  1. _____ One mole of a monatomic ideal gas with Cv,m = 1.5 R at 1.0 atm and 273.15 K is put through the reversible cycle process as follows: 1. isobaric expansion to double its volume; 2. isochoric reduction of pressure to half its initial value; 3. isothermal compression back to its original state. Consider the following statements: A) w = 0 for the isochoric process B) Δ U = 0 for the isothermal process C) Δ H = 0 for the isobaric process D) Δ G = w for the isothermal process E) Δ S = 8.64 J/K for the isobaric process F) Δ G = ΔA for the isothermal process

Which of the above statements are correct?

  1. A, B, C; 2) A, D, E; 3) A, B, D, F; 4) B, E; 5) A, C, F;
  1. _____ A reaction is spontaneous if: I) ΔG is a negative value II) Both enthalpy and entropy increase III) ΔH is negative and ΔS is positive IV) Both enthalpy and entropy decrease V) ΔH is positive and ΔS is negative Which of the above statements are correct? A) I and II B) I and III C) II and V D) III and IV E) Cannot be determined without the temperature
  2. _____ The molar entropy of 2.0 mole of hydrogen gas with Cp,m = 28.824 J mol-1^ K-1^ at P = 1.0 bar and T = 298 K is 130.684 J mol-1^ K-1. Calculate its molar entropy at 350 K and P = 1.0 bar. A) 165 J mol-1^ K- B) 135 J mol-1^ K- C) 270 J mol-1^ K- D) 153 J mol-1^ K- E) none of these
  1. (30 points) The heat capacities of the solid and liquid forms of a compound A are respectively 18.3 and 25.2 – 0.0032 T cal mol-1^ K-1. The compound melts under 1 atm pressure at a temperature of 160 °C with a heat of fusion of 2460 cal mol-1. What are the ΔH, ΔS, and ΔG of the process 3A ( l ) → 3A (s) at 145 °C and 1 atm?
  1. (24 points) A sample of 4.0 mol of O 2 is originally confined in 20 dm^3 at 270 K and then undergoes adiabatic expansion against a constant pressure of 600 Torr until the volume has increased by a factor of 3.0. Calculate q, w, ΔT, ΔU, ΔH and ΔS. (The final pressure of the gas is not necessarily 600 Torr.) [1 dm^3 = 1 L; the Cp,m for O 2 is 29.355 J K-1^ mol-1]