Chemical Thermodynamics
Chemical Thermodynamics
Chemical Thermodynamics
Long Test
Directions: Read each statement carefully, and then choose the letter of the correct answer.
15. Which of the following reactions is likely to have the most positive change in
entropy?
a. N2(g) + 3H2(g) → 2NH3(g)
b. N2(g) + 2O2(g) → 2NO2(g)
c. 2C(s) + O2(g) → 2CO(g)
d. C(s) + O2(g) → CO2(g)
e. Cano(s) + CO2(g) → CaCO3(s)
16. For which of the following reactions will the entropy of the system decrease?
a. 2NH3(g) → N2(g) + 3H2(g)
b. 2C(s) + O2(g) → 2CO(g)
c. CaCO3(s) → Cano(s) + CO2(g)
d. 2NO2(g) → N2O4(g)
e. Nao(s) → Na+(as) + OH–(as)
17. All of the following statements are true EXCEPT
a. For a given material, the gas has greater entropy than the solid.
b. The entropy for gaseous elements is zero at 298 K.
c. At 0 K, an ordered pure crystalline solid has an entropy of zero.
d. For a given material, the liquid has greater entropy than the solid.
e. Increasing the temperature of a substance increases its entropy.
18. All of the following statements are true EXCEPT
a. A reaction is spontaneous if ΔG < 0.
b. If ΔG = 0, the system is at equilibrium.
c. If ΔG = 0, then ΔS = ΔH.
d. If ΔG > 0, then a reaction is not spontaneous.
e. ΔG is referred to as Gibbs free energy.
23. At what temperatures will a reaction be spontaneous if ΔH° = +62.4 kJ and ΔS°
= +301 J/K?
a. All temperatures below 207 K.
b. All temperatures above 207 K.
c. Temperatures between 179 K and 235 K.
d. The reaction will be spontaneous at any temperature.
e. The reaction will never be spontaneous.
24. Which of the following are conditions for the standard Gibbs free energy?
1. Ions or molecules in solution are present at one molar concentrations.
2. Gases are present at one atmosphere partial pressure.
3. The temperature of the system is 273 K.
a. 1 only
b. 2 only
c. 3 only
d. 1 and 2
e. 1, 2, and 3
25. What is the correct form for the Gibbs-Helmholtz equation?
a. ΔG = ΔH − TΔS
b. ΔG = ΔH + TΔS
c. ΔH = ΔG − TΔS
d. ΔS = ΔH − TΔG
e. ΔG = ΔS – TΔH
29. At 298 K, all of the following substances have a standard free energy of
formation of zero EXCEPT ____.
a. Br2(g)
b. I2(s)
c. S8(s)
d. Cl2(g)
e. Hg(l)
30. For the decomposition of hydrogen peroxide to water and oxygen,
H2O2 (g) → H2O (g) + 1/2 O2 (g)
ΔH° = −106 kJ, and ΔS° = +0.0580 kJ/K. In what temperature range is the
reaction spontaneous (ΔG° < 0)?
a. The temperature must be greater than 1.83 × 103 K.
b. The temperature must be less than 1.83 × 103 K.
c. The temperature must be between 225 K and 1.83 × 103 K.
d. ΔG° is always less than zero.
e. ΔG° is never less than zero.
31. In a gas phase reaction, what is the effect of increasing reactant or product
pressure on the standard Gibbs free energy, ΔG°?
a. ΔG° increases due to decreased entropy.
b. ΔG° decreases due to decreased entropy.
c. ΔG° increases due to increased enthalpy.
d. ΔG° may either increase or decrease.
e. ΔG° is unchanged.
32. The standard free energy change for a chemical reaction is +13.3 kJ. What is the
equilibrium constant for the reaction at 125°C? (R = 8.31 × 10−3kJ/K)
a. 2.8 × 10–6
b. 2.0 × 10–5
c. 4.7 × 10–3
d. 1.8 × 10–2
e. 2.1 × 102