Name:    Entropy&FreeEnergy

Multiple Choice
Identify the letter of the choice that best completes the statement or answers the question.

1.

Which reaction is likely to have a negative change in entropy?
 a. 2 NH3(g) → N2(g) + 3 H2(g) b. CaCO3(s) →CaO(s) + CO2(g) c. NaCl(s) → Na+(aq) + Cl-(aq) d. N2O4(g) → 2 NO2(g) e. 2 CO(g) → C(s) + O2(g)

2.

Calculate the standard entropy change for the combustion of methanol at 25 °C.

2 CH3OH(l) + 3 O2(g) 2 CO2(g) + 4 H2O(g)

 Species S° (J/K×mol) CH 3 OH (l) 127.2 O 2 (g) 205.1 CO 2 (g) 213.7 H 2 O(g) 188.8
 a. -2052.3 J/K b. -312.9 J/K c. +70.2 J/K d. +312.9 J/K e. +2052.3 J/K

3.

Calculate the standard entropy change for the following reaction,

2 HgO(s) 2 Hg(l) + O2(g)

given S°[HgO] = 70.3 J/K·mol, S°[ Hg(l)] =76.0 J/K·mol, and S°[O2(g)] = 205.1 J/K·mol.
 a. -216.5 J/K b. +210.8 J/K c. +216.5 J/K d. +351.4 J/K e. +497.7 J/K

4.

The standard entropy of formation of PCl3(g) is -33.2 J/K·mol.

1/4 P4(s) + 3/2 Cl2(g) PCl3(g)

Calculate the standard molar entropy of PCl3(g) given S°[P4(s)] = 41.1 J/K·mol and S°[Cl2(g)] = 223.1 J/K·mol.
 a. -378.1 J/K·mol b. -297.4 J/K·mol c. +212.2 J/K·mol d. +231.0 J/K·mol e. +311.7 J/K·mol

5.

For the following reaction at 25.0 °C,

2 C(s) + O2(g) 2 CO(g)

calculate given = 179.1 J/K and = -221.1 kJ.
 a. -9023 J/K b. -562.3 J/K c. -167.7 J/K d. +170.2 J/K e. +920.7 J/K

6.

Use the following thermodynamic data

 Species Δ H° (kJ/mol) S° (J/K·mol) H 2 O 2 (l) -187.78 109.6 H 2 O(l) -285.83 69.91 O2 (g) 0 205.14

to calculate for the decomposition of hydrogen peroxide at 25.0 °C.

2 H2O2(l) 2 H2O(l) + O2(g)
 a. -783.5 J/K b. -531.9 J/K c. +494.2 J/K d. +783.5 J/K e. +3741 J/K

7.

Predict the signs of ΔH and ΔS for the condensation of steam at 85 °C.
 a. ΔH < 0 and ΔS < 0 b. ΔH < 0 and ΔS > 0 c. ΔH > 0 and ΔS < 0 d. ΔH > 0 and ΔS > 0 e. ΔH = 0 and ΔS < 0

8.

Hydrogen gas is a non-polluting fuel. Predict the signs of ΔH, ΔS, and ΔG for the combustion of hydrogen gas at 150 °C.

2 H2(g) + O2(g) 2 H2O(g)
 a. ΔH < 0, ΔS > 0, ΔG < 0 b. ΔH < 0, ΔS < 0, ΔG < 0 c. ΔH < 0,ΔS > 0, ΔG < 0 d. ΔH > 0, ΔS < 0, ΔG < 0 e. ΔH > 0, ΔS < 0,ΔG > 0

9.

Diluting concentrated sulfuric acid with water can be dangerous. The temperature of the solution can increase rapidly. What are the signs of ΔH, ΔS, and ΔG for this process?
 a. ΔH < 0, ΔS > 0, ΔG < 0 b. ΔH < 0, ΔS < 0, ΔG < 0 c. ΔH < 0, ΔS > 0, ΔG > 0 d. ΔH > 0, ΔS > 0, ΔG < 0 e. ΔH > 0, ΔS < 0, ΔG > 0

10.

At what temperatures will a reaction be spontaneous if ΔH = +158 kJ and ΔS = +411 J/K?
 a. All temperatures below 384 K b. Temperatures between 158 K and 411 K c. All temperatures above 384 K d. The reaction will be spontaneous at any temperature. e. The reaction will never be spontaneous.

11.

At what temperatures will a reaction be spontaneous if ΔH = -76.0 kJ and ΔS = +231 J/K?
 a. All temperatures below 329 K b. Temperatures between 0 K and 231 K c. All temperatures above 329 K d. The reaction will be spontaneous at any temperature. e. The reaction will never be spontaneous.

12.

For a reaction, ΔH = +62.9 kJ andΔS = +132.9 J/K. At what temperature will ΔG = 0.00 kJ?
 a. 2.11 K b. 70.0 K c. 473 K d. 8.36 ´ 106 K e. DG is greater than 0.00 kJ at any temperature.

13.

Calculate for the reaction below at 25.0 °C

2 H2O(g) + S(s) 2 H2S(g) + O2(g)

given = +442.4 kJ and = +206.9 J/K.
 a. +380.7 kJ b. +504.1 kJ c. +649.3 kJ d. +1277.7 kJ e. +6.125 ´ 104 kJ

14.

Calculate for the reaction below at 25.0°C

CO(g) + H2O(l) H2(g) + CO2(g)

given [CO(g)] = -137.2 kJ/mol, [H2O(l)] = -237.2 kJ/mol, [H2(g)] = 0.0 kJ/mol, and [CO2(g)] = -394.4 kJ/mol.
 a. -768.8 kJ b. -294.4 kJ c. -20.0 kJ d. +20.0 kJ e. +768.8 kJ

15.

The for the following reaction is +70.9 kJ.

SO3(g) SO2(g) + O2(g)

Given [ SO3(g)] = -371.0 kJ/mol, calculate [SO2(g)].
 a. -300.1 kJ/mol b. -5.23 kJ/mol c. +5.23 kJ/mol d. +300.1 kJ/mol e. +441.9 kJ/mol

16.

Calculate DG° for the reaction below at 25.0 °C.

P4(s) + 6 H2O(l) 4 H3PO4(l)

 Species (kJ/mol) (J/K· mol) P 4 (s) 0 22.80 H 2 O(l) -285.8 69.95 H3 PO 4 (l) -1279.0 110.5
 a. -993.2 kJ b. -998.5 kJ c. -3137 kJ d. -3252 kJ e. -3401 kJ

17.

Calculate ΔG° for the reaction below at 125 °C.

C2H5OH(g) + 3 O2(g) 2 CO2(g) + 3 H2O(g)

 Species (kJ/mol) (J/K· mol) C 2 H 5 OH(g) -235.3 282.7 O 2 (g) 0 205.1 CO 2 (g) -393.5 213.7 H 2 O(g) -241.8 188.8
 a. -366.0 kJ b. -1277.1 kJ c. -1289.1 kJ d. -1315.2 kJ e. -3.94 ´ 104 kJ

18.

Estimate the boiling point of carbon tetrachloride given the following thermodynamic parameters.

 CCl 4 (l) CCl 4 (g) (kJ/mol) -128.4 -96.0 ( J/K·mol) 214.4 309.7 (kJ/mol) -57.6 -53.6
 a. -272 °C b. 25 °C c. 67 °C d. 69 °C e. 109 °C

19.

For a chemical reaction, if ΔG° = 0, then
 a. K > 1 b. K = 0 c. K < 1 d. K < 0 e. K = 1

20.

All of the following relationships are true EXCEPT
 a. = - T b. = -RT ln (K) c. = + d. DH = + RT ln (K) e. = -T

21.

The standard free energy change for a chemical reaction is -18.3 kJ/mole. What is the equilibrium constant for the reaction at 87 °C? (R = 8.314 J/K·mol)
 a. 2.2 ×10-3 b. 1.0 c. 6.1 d. 4.5 × 102 e. 1.3 × 106

22.

The standard free energy change for the formation of N2H4(l) from elements is +149 kJ/mol at 25 °C. What is the equilibrium constant for the reaction? (R = 8.314 J/K·mol)
 a. 7 ｘ10-61 b. 8 ｘ 10-27 c. 1 d. 1 ｘ 1026 e. 1 ｘ 1060

23.

What is the equilibrium constant for reaction below at 25 °C? (R = 8.314 J/K·mol)

2 H2O2(l)  ⇌ 2 H2O(l) + O2(g)

given [H2O2(l)] = -120.3 kJ/mol, [H2O(l)] = -237.1 kJ/mol, and [O2(g)] = 0.0 kJ/mol.
 a. 5 ｘ10-95 b. 1 ｘ10-41 c. 1 d. 3 ｘ 1020 e. 9 ｘ1040

24.

The equilibrium constant for a reaction at 25 °C is 4.7 x 10-8. What is DG°? (R = 8.314 J/K·mol)
 a. +1.52 kJ b. +3.51 kJ c. +6.81 kJ d. +18.2 kJ e. +41.8 kJ

25.

Calculate ΔG° for the following reaction at 425 °C,

H2(g) + I2(g)   2 HI(g)

given K = 56. (R = 8.314 J/K·mol)
 a. -23.4 kJ b. -14.2 kJ c. -10.1 kJ d. -6.18 kJ e. +14.2 kJ