# Kinetics and Equilibrium

1. The equilibrium constant for the following reaction is 5.0 Ã- 108 at 25Â°C.

N2 (g) + 3H2 (g) &#8594; 2NH3 (g) The value of &#916;GÂ° for this reaction is __________ kJ/mol.

A) -4.2
B) -22
C) 22
D) -50
E) -25

2. The equilibrium constant for a certain reaction is 0.705 at 298 K and 0.321 at 400 K. Which statement is correct?
A) The equilibrium constant cannot become smaller if the temperature is increased.
B) The reaction is endothermic.
C) The reaction is not spontaneous at any temperature if the standard entropy of reaction is negative.
D) The reaction is not spontaneous at any temperature if the standard entropy of reaction is positive.
E) The reaction is spontaneous at all temperatures if the standard entropy of reaction is positive.
3. Which of the following statements is true regarding the impact of additional chemicals on the solubility of a saturated solution of CaCO3?
A) CaCl2 will decrease its solubility; NaOH will increase its solubility.
B) HCl will decrease its solubility; CaCl2 will increase its solubility.
C) CaCl2 will decrease its solubility; HCl will increase its solubility.
D) NaCl will decrease its solubility; HCl will increase its solubility.
4. In glycolysis, the hydrolysis of phosphoenol pyruvate is thermodynamically driven by the highly exergonic enol-to-keto conversion of pyruvate. From the two half reactions shown below, what is the GÂ° (kJ/mol) of the overall reaction?

Half reactions:

I. phosphoenol pyruvate + H2O &#8594; enol pyruvate + HPO42- GÂ° = -16 kJ/mol

II. keto pyruvate &#8594; enol pyruvate GÂ° = 49.5 kJ/mol

Overall reaction: phosphoenolpyruvate + H2O &#8594; keto pyruvate + HPO42-

A) 61.9
B) 29.9
C) -29.9
D) -61.9
E) 123.8
5. An exothermic chemical reaction in which 2 moles of gaseous products are formed from 3 moles of gaseous reactants is favored by:
A) increasing both temperature and pressure.
B) increasing temperature and decreasing pressure.
C) decreasing both temperature and pressure.
D) decreasing temperature and increasing pressure.
E) none of the above changes.
6. Given the thermodynamic data in the table below, calculate the equilibrium constant for the reaction:

2SO2 (g) + O2 &#8594; (g) 2SO3 (g)

Substance &#916;HfÂ° (kJ/mol) &#916;SÂ° (J/mol K)

SO2 (g) -297 249

O2 (g) 0 205

SO3 (g) -395 256

A) 3.82 Ã- 1023
B) 1.06
C) 1.95
D) 32 Ã- 1024
E) More data are needed.
7. &#916;S will be positive for which of the following reactions?

I. BaF2 (s) &#8594; Ba2+ (aq) + 2F- (aq)

II. CO2 (g) &#8594; CO2 (s)

III. 2 NO2 (g) &#8594; N2O4 (g)

IV. 2 NH3 (g) &#8594; N2 (g) + 3 H2 (g)

V. 2 H2 (g) + O2 (g) &#8594; 2 H2O (g)

A) I and II
B) II and III
C) I and IV
D) IV and V
E) III and V
8. For the following reaction:

Ag2O (s) &#8594; Ag (s) + Â½O2 (g)

HÂ°f (kJ / K . mole) -31 0 0

SÂ° (J / K . mole) 121.3 42.6 205.1

Calculate Kp at 25 Â°C.

A) 2.22 x 10-3
B) 2.22 x 10-2
C) 1.09 x 10-2
D) 4.41 x 10-1
9. Under which temperature conditions will the following reaction be spontaneous?

A (aq) + B (aq) &#8594;C (s) + D (aq) &#916;HÂ°= -34.0 kJ/mol

&#916;SÂ° = -57.0 J/mol?K

A) above 273Â°C
B) below 323Â°C
C) above 552Â°C
D) below 705Â°C
E) At all temperatures.
10. Which of the following statements is false?
A) For a reaction at equilibrium, &#916;G = 0.
B) All reactions in which the entropy of the universe increases are product-favored.
C) All reactions in which the entropy of the system increases are product-favored.
D) Some reactions that are product-favored at room temperature may not be product-favored at higher temperatures.
E) It is possible for a reactant-favored process to proceed to the product side, but only if it is continuously fueled by some other source of free energy, such that the combined &#916;G is negative and the overall entropy of the universe still increases.
11. What is the value of &#916;GÂ° (in kJ/mol) for this reaction at 25Â°C?

A (g) &#8594; B (g) &#916;HÂ° = -42.4 kJ/mol &#916;SÂ°= -56 J/mol?K

A) -136
B) +236
C) -26
D) -59
E) none of the above
12. Which of the following reactions have a decrease in entropy?

I. H2O (l) &#8594; H2O (g)

II. 2 H2 (g) + O2 (g) &#8594; 2 H2O (g)

III. MgO (s) + CO2 (g) &#8594; MgCO3 (g)

IV. PCl5 (s) &#8594; PCl3 (l) + Cl2 (g)

A) I and II
B) II and III
C) III and IV
D) I and III.
E) II and IV.
13. For the following reaction:

Ag2O (s) &#8594; Ag (s) + Â½O2 (g)

HÂ°f (kJ / K . mole) -31 0 0

SÂ° (J / K . mole) 121.3 42.6 205.1

Calculate the temperature (Â°C) where Kp = 1.

A) 152
B) 194
C) 222
D) 367
14. For the following reaction:

CO (g) + 2 H2 (g) &#8594; CH3OH (g)

What are the units for Kp?

A) No units
B) atm.
C) atm-1
D) atm-2
15. Calculate G (kJ/mol) for the reaction using the listed [GÂºf values]:

P2 (g) [103.7] + O2 (g) + 3Cl2 (g) &#8594; 2POCl3 (g) [-502.5]

A) 1,109
B) -1,005
C) -606.2
D) 606.2
E) -1109
16. The equilibrium constant for a reaction is 0.50 at 30Â°C. What is the value of &#916;GÂ° (kJ/mol) at this temperature?
A) -4.1
B) 4.1
C) 1.4 Ã- 102
D) 1.7
17. Which one of the following cannot be determined using thermodynamics?
A) the direction of a spontaneous reaction
B) the temperature at which a reaction will be spontaneous
C) the extent of a reaction
D) the rate of a reaction
E) the value of the equilibrium constant.
18. Which of the following statements is true when you consider the following reaction:

A + B &#8594; C + D?

A) If &#916;H<0 and &#916;S<0, then the reaction is product-favored at all temperatures.
B) If &#916;H<0 and &#916;S<0, then the reaction is never product-favored at any temperature.
C) If &#916;H<0 and &#916;S<0, then the reaction is product-favored at high temperatures but not at low temperatures.
D) If &#916;H<0 and &#916;S<0, then the reaction is product-favored at low temperatures but not at high temperatures.
19. Consider a pure, crystalline solid being heated from absolute zero to some very high temperature. Which one of the following processes produces the greatest increase in the entropy of the substance?
A) Melting the solid
B) Heating the liquid
C) Heating the gas
D) Heating the solid
E) Boiling the liquid
20. Calculate the entropy change (J/mole.K) of the reaction. The molar entropies [S] are given in brackets after each substance.

2C2H2 (g) [200.8] + 5 O2 (g) [205.0] &#8594; 4 CO2 (g) [213.6] + 2H2O (l) [69.91]

A) -432.4
B) -122.3
C) 122.3
D) 432.4
E) 689.3

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Jennifer Fronteras, MSc

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Active since 2009

BSc, Visayas State College of agriculture (now Visayas State University)
MSc, University of the Philippines Los Banos

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