Equilibrium 1. For a chemical reaction at equilibrium, the relationship between the rate constants for the forward and reverse reactions (kf and kr) and the equilibrium constant for the process (Keq) is kf

AB A. Keq = kf kr

kr

B. Keq = kf  kr C. Keq = kf + kr D. Keq = kf / kr E. Keq = kr / kf

2.

Which of the following will change the value of an equilibrium constant? 1. changing temperature 2. adding a catalyst 3. varying the initial concentration of reactants A. B. C. D. E.

3.

1 only 2 only 1 and 2 1 and 3 all three

Kc for the reaction HCl(g) + NH3(g) A.

NH 4 Cl HClNH 3 

B.

HClNH 3  NH 4 Cl

C.

HClNH 3 

D.

[HCl] [NH3]

E.

[NH4Cl]

1

NH4Cl(s) is

4.

Consider the following three reactions: 1.

H2(g) + Cl2(g)

2 HCl(g)

2.

C(s) + H2O(g)

CO(g) + H2(g)

3.

Fe3O4(s) + 4H2(g)

3 Fe(s) + 4H2O(g)

For which of these would Kp = Kc? A. B. C. D. E.

5.

1 only 1 and 2 only 1 and 3 only 3 only 2 and 3 only

At 50C, Kc = 2.2  103 for the reaction 3 Fe(s) + 4 H2O(g)

Fe3O4(s) + 4 H2(g)

What is the value of Kp at 200C for this reaction? A. B. C. D. E.

6.

8.8  103 2.2  103 5.5  102 3.5  104 This question cannot be answered with the information provided

For the following reaction, Kp = 1.96 at 700 K. NOCl(g)

NO(g) + 1/2 Cl2(g)

What is Kp for the reaction below at this same temperature? Cl2(g) + 2 NO(g) A. B. C. D. E.

2 NOCl (g)

1.96 3.85 0.260 0.509 None of the above is within 5% of the correct answer.

7.

When solid NH4HS is placed in a closed, evacuated flask at 28°C, the solid dissociates according to the equation: NH4HS(s)

NH3(g) + H2S(g).

The total pressure of the equilibrium mixture is 0.766 atm. Determine Kp at this temperature A B C D E

8.

0.147 0.383 0.587 0.766 6.80

Kc for the reaction below equals 125 at a particular temperature. F2(g) + Cl2(g)

2 FCl(g)

Suppose a system involving this reaction is already at equilibrium and the concentrations of F2 and Cl2 are found to be [F2] = 0.115 M and [Cl2] = 0.221 M. What is the concentration of FCl in the system? A. B. C. D. E.

9.

[FCl] = 2.54  102 M [FCl] = 3.17 M [FCl] = 1.78 M [FCl] = 1.43  102 M None of the above is within 5% of the correct answer

At a certain temperature, 0.300 moles of NO, 0.200 moles of Cl2, and 0.500 moles of ClNO were placed in a 25.0 L vessel and allowed to reach equilibrium: 2 NO(g) + Cl2(g)

2 ClNO(g).

At equilibrium, 0.600 moles of ClNO were present. The number of moles of Cl2 present at equilibrium is A. B. C. D. E.

0.100 0.150 0.200 0.250 0.300

10.

Consider the reaction 2 NH3(g) N2(g) + 3 H2(g). Suppose 6 moles of pure NH3 are placed in a 1.0–liter flask and allowed to reach equilibrium. If X represents the concentration in moles per liter of N2 present in the system once equilibrium is reached, which one of the following will represent the concentration of NH3 at equilibrium in moles per liter? A. B. C. D. E.

11.

6 – (X/2) 6–X 6 – 2X 3 – 2X None of the above is correct

For the following reaction Kc = 4.0 at a particular temperature. N2(g) + O2(g)

2 NO(g)

Suppose we begin an experiment by mixing 1.0 mol of N2 and 1.0 mol of O2 in a 1.0–liter container. What will the concentration of NO be once equilibrium is reached at the given temperature? A. B. C. D. E.

12.

[NO] = 0.25 M [NO] = 0.50 M [NO] = 0.67 M [NO] = 1.0 M None of the above is within 5% of the correct answer

At 750C, Kp = 0.770 for the reaction H2(g) + CO2(g)

H2O(g) + CO(g)

If 0.200 atm of H2 and 0.200 atm of CO2 are admitted into a rigid container and allowed to reach equilibrium, what will the equilibrium partial pressure of CO be? A. B. C. D. E.

13.

0.0935 atm 0.109 atm 1.43 atm 0.100 atm 0.770 atm

At high temperatures one mole of hydrogen gas reacts with one mole of bromine gas to form hydrogen bromide. At a given temperature the equilibrium constant is 57.6. If at the same temperature, a mixture of 4.67  103 M bromine gas, 2.14  103 hydrogen gas, and 2.40  102 M hydrogen bromide gas is made, then A. B. C. D. E.

the system is at equilibrium. the system is far from equilibrium and will shift to form more hydrogen gas. the system is far from equilibrium and will shift to form more hydrogen bromide gas. nothing can be deduced since we do not know whether the reaction is endothermic or exothermic. nothing can be deduced since we do not know whether the equilibrium constant is Kc or Kp.

14.

15.

Which one of the following equilibriums is least affected by a change in the volume of the system? A.

2 C(s) + O2(g)

2 CO(g)

B.

2 NO2(g)

C.

H2(g) + S()

D.

H2O()

E.

2 NO(g) + Cl2(g)

N2O4(g) H2S(g) H2O(g) 2 NOCl(g)

Nickel (II) oxide can be reduced to nickel metal by treatment with carbon monoxide as indicated in the reaction CO(g) + NiO(s)

CO2(g) + Ni(s)

Kp=20 at 500C

If the reaction chamber contains some solid Ni and NiO, 400 mm Hg of CO2 and 20 mm Hg of CO, all at equilibrium, which one of the following changes will lead to the reduction of more nickel oxide at 500C? A. B. C. D. E.

Doubling the amount of NiO(s) present. Adding CO2 to raise its pressure to 700 mm Hg. Adding CO to raise its pressure to 40 mm Hg. Removal of half of the NiO(s) present. Doubling the volume of the reaction chamber at 500C.

16. For the reaction FeO(s) + CO(g) Fe(s) + CO2(g), A. the usual expression for the equilibrium constant is Kc = B.

addition of CO2(g) will increase Kc.

C.

increasing the volume of an equilibrium mixture at constant temperature will cause the number of moles of CO2 to increase as the mixture re–equilibrates.

D.

adding more FeO to an equilibrium mixture will cause the number of moles of CO2 to increase as the system re–equilibrates.

E.

None of the above statements is true