Question 1

For the reaction $$\mathrm{H_2$(g) + I_2$(g) \rightleftharpoons 2HI(g)}$$, if $$K_c = 54 at 700 K$$, what is the value of $$K_c$$ for the reverse reaction $$\mathrm{2HI(g) \rightleftharpoons H_2$(g) + I_2$(g)}$$?

Accepted Answer

$$K_c = 0.018$$

Question 2

If the equilibrium constant for $$\mathrm{H_2$(g) + I_2$(g) \rightleftharpoons 2HI(g)} is$$ $$K_c = 54$$, what is the equilibrium constant for $$\mathrm{2H_2(g) + 2I_2(g) \rightleftharpoons 4HI(g)}$$?

Accepted Answer

$$K_c = 2.9 	imes 10^3$

Question 3

Given the following reactions and their equilibrium constants:

$$\mathrm{2NOBr(g) \rightleftharpoons 2NO(g) + Br_2$(g)},\ K_{c1} = 0.014$$

$$\mathrm{Br_2$(g) + Cl_2$(g) \rightleftharpoons 2BrCl(g)},\ K_{c2} = 7.2$$

What is the equilibrium constant for the reaction $$\mathrm{2NOBr(g) + Cl_2$(g) \rightleftharpoons 2NO(g) + 2BrCl(g)}$$?

Accepted Answer

$$K_c = 0.10$$

Question 4

Which of the following statements about equilibrium constants is TRUE?

Accepted Answer

Equilibrium constants are dimensionless quantities called activities.

Question 5

For the reaction $$\mathrm{$$CaCO_3$$(s) \rightleftharpoons CaO(s) + CO_2$(g)}$$, which substances appear in the equilibrium constant expression?

Accepted Answer

$$\mathrm{CO_2$(g)}$$ only

Question 6

A mixture of $$0.100$$ mol NO, $$0.050$$ mol H$$_2$$, and $$0.100$$ mol H$$_2O is $$placed in a $$1.00 L $$vessel at $$300 K. At $$equilibrium, $$[NO] = 0.062 M $$for the reaction $$2NO(g) + 2H_2(g) \rightleftharpoons N_2$(g) + 2H_2O(g). $$What is the value of $$K_c$$?

Accepted Answer

$$K_c = 654$$

Question 7

For the decomposition of BrCl: $$2\mathrm{BrCl(g)} \rightleftharpoons \mathrm{Br_2$(g)} + \mathrm{Cl_2$(g)}$$, if the initial pressure of BrCl is $$0.500$$ atm and the equilibrium pressure is $$0.040$$ atm, what is the value of $$K_p$$?

Accepted Answer

$$K_p = 0.021$$

Question 8

For the reaction $$\mathrm{Br_2$(g) + Cl_2$(g) \rightleftharpoons 2BrCl(g)}$$ with $$K_p = 7.0 at$$ $$400 K$$, if the initial partial pressure of BrCl is $$1.00$$ atm and the system is allowed to reach equilibrium, which of the following is closest to the equilibrium pressure of BrCl?

Accepted Answer

$$0.57$$ atm

Question 9

Methane reacts with iodine: $$\mathrm{CH_4$(g) + I_2$(g) ightleftharpoons CH_3I(g) + HI(g)}. At$$ $$630 K$$, $$K_p = 2.26 	imes 10$$^{-4}$$. If the initial partial pressures are 105$ torr CH_4$ and 80.0$ torr I_2$, what is the equilibrium partial pressure of HI? (1 atm = 760 torr)

Accepted Answer

$$0.00178$$ atm

Question 10

Which of the following best describes what happens to the amount of CaCO$$_3(s) if $$some CO$$_2(g) is $$released from a sealed system at equilibrium for $$\mathrm{$$CaCO_3$$(s) \rightleftharpoons CaO(s) + CO_2$(g)}$$ and then the seal is restored?

Accepted Answer

The amount of CaCO$$_3(s) $$increases.

Question 11

Which of the following starting mixtures will NOT allow the system $$\mathrm{$$CaCO_3$$(s) \rightleftharpoons CaO(s) + CO_2$(g)} to $$attain equilibrium?

Accepted Answer

CaO(s) and CO$$_2(g) at a $$pressure greater than $$K_p$$

Question 12

Which of the following is omitted from the equilibrium constant expression for the reaction $$\mathrm{NH_3$(aq) + H_2O(l) \rightleftharpoons NH_4$^+(aq) + OH^-(aq)}$$?

Accepted Answer

$$\mathrm{H_2O(l)}$$

Question 13

If the equilibrium constant $$K$$ for a reaction is much greater than 1, what does this indicate about the position of equilibrium?

Accepted Answer

The reaction favors the products.

Question 14

Which of the following best explains why pure solids and liquids are omitted from equilibrium constant expressions?

Accepted Answer

Their activities are defined as 1.

Question 15

A reaction has $$K_c = 1.2 	imes 10$$^{-5}$$. Which statement is correct?

Accepted Answer

At equilibrium, reactants are favored.

Question 16

If a reaction is multiplied by a factor of 3, how is the new equilibrium constant $$K'_{c}$$ related to the original $$K_c$$?

Accepted Answer

$$K'_c = K_c^3$

Question 17

Which of the following is a correct equilibrium constant expression for the reaction $$\mathrm{Cr(s) + 3Ag^+(aq) \rightleftharpoons Cr$$^{3+}$$(aq) + 3Ag(s)}$$?

Accepted Answer

$$K_c = \dfrac{[Cr$$^{3+}$$]}{[Ag^+]^3}$$

Manipulating Chemical Equilibria and Calculating Equilibrium Constants

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