Q: Consider the reaction $$\mathrm{NO_2$\ (g)} + \mathrm{N_2O\ (g)} \rightleftharpoons 3\ \mathrm{NO\ (g)}$$ with $$K_c = 7.32 \times 10$$^{-2}$$. If the initial concentrations are $$[\mathrm{$$NO_2$$}] = 1.38\ \mathrm{M}$$ and $$[\mathrm{N_2O}] = 2.24\ \mathrm{M}$$, and $$[\mathrm{NO}]$$ at equilibrium is 0.489$$\ \mathrm{M}$$, what is the value of K_c$ under these conditions?

$$K_c = 7.32 \times 10$$^{-2}$$

Question 1

For the reaction $$4\ \mathrm{NO\ (g)} + 6\ \mathrm{H_2O\ (g)} \rightleftharpoons 4\ \mathrm{NH_3$\ (g)} + 5\ \mathrm{O_2$\ (g)}$$, which of the following is the correct equilibrium expression for $$K_c$$?

Accepted Answer

$$K_c = \dfrac{[\mathrm{NH_3$}]^4 [\mathrm{O_2$}]^5}{[\mathrm{NO}]^4 [\mathrm{H_2O}]^6}$$

Question 2

Given the equilibrium concentrations $$[\mathrm{NH_3$}] = 0.17\ \mathrm{M}$$, $$[\mathrm{O_2$}] = 0.39\ \mathrm{M}$$, $$[\mathrm{NO}] = 2.36 	imes 10$$^{-2}$$\ \mathrm{M}$$, and $$[\mathrm{H_2O}] = 9.98 	imes 10$$^{-3}$$\ \mathrm{M}$$, calculate the value of $$K_c$$ for the reaction $$4\ \mathrm{NO\ (g)} + 6\ \mathrm{H_2O\ (g)} ightleftharpoons 4\ \mathrm{NH_3$\ (g)} + 5\ \mathrm{O_2$\ (g)}.$$

Accepted Answer

$$K_c = 2.1 	imes 10^7$

Question 3

For the reaction $$4\ \mathrm{NO\ (g)} + 6\ \mathrm{H_2O\ (g)} \rightleftharpoons 4\ \mathrm{NH_3$\ (g)} + 5\ \mathrm{O_2$\ (g)}$$, if $$K_c is $$very large, what does this indicate about the position of equilibrium?

Accepted Answer

The reaction favors the formation of products.

Question 4

Given the reaction $$4\ \mathrm{NO\ (g)} + 6\ \mathrm{H_2O\ (g)} \rightleftharpoons 4\ \mathrm{NH_3$\ (g)} + 5\ \mathrm{O_2$\ (g)}$$, which of the following is the correct equilibrium expression for $$K_p$$?

Accepted Answer

$$K_p = \dfrac{(P_{\mathrm{NH_3$}})^4$ (P_{\mathrm{O_2$}})^5$}{(P_{\mathrm{NO}})^4$ (P_{\mathrm{H_2O}})^6$}$$

Question 5

If the reaction $$4\ \mathrm{NO\ (g)} + 6\ \mathrm{H_2O\ (g)} \rightleftharpoons 4\ \mathrm{NH_3$\ (g)} + 5\ \mathrm{O_2$\ (g)} is $$reversed, how does the new equilibrium constant $$K'_c$$ relate to the original $$K_c$$?

Accepted Answer

$$K'_c = \dfrac{1}{K_c}$$

Question 6

If the reaction $$4\ \mathrm{NO\ (g)} + 6\ \mathrm{H_2O\ (g)} \rightleftharpoons 4\ \mathrm{NH_3$\ (g)} + 5\ \mathrm{O_2$\ (g)} is $$multiplied by $$\dfrac{9}{4}$$, how does the new equilibrium constant $$K''_c$$ relate to the original $$K_c$$?

Accepted Answer

$$K''_c = (K_c$$)^{9/4}$$

Question 7

Consider the reaction $$\mathrm{NO_2$\ (g)} + \mathrm{N_2O\ (g)} ightleftharpoons 3\ \mathrm{NO\ (g)}$$ with $$K_c = 7.32 	imes 10$$^{-2}$$. If the initial concentrations are $$[\mathrm{$$NO_2$$}] = 1.38\ \mathrm{M}$$ and $$[\mathrm{N_2O}] = 2.24\ \mathrm{M}$$, and $$[\mathrm{NO}]$$ at equilibrium is 0.489$$\ \mathrm{M}$$, what is the value of K_c$ under these conditions?

Accepted Answer

$$K_c = 7.32 	imes 10$$^{-2}$$

Question 8

For the heterogeneous reaction $$\mathrm{SO_3$\ (g)} + \mathrm{H_2O\ (l)} \rightleftharpoons \mathrm{H_2SO_4\ (aq)}$$, which of the following is the correct equilibrium expression for $$K_c$$?

Accepted Answer

$$K_c = [\mathrm{H_2SO_4}] / [\mathrm{SO_3$}]$$

Question 9

For the reaction $$\mathrm{Ru$$^{3+}$$\ (aq)} + 3\ \mathrm{Br^-\ (aq)} \rightleftharpoons \mathrm{$$RuBr_3$$\ (s)}$$, which of the following is the correct equilibrium expression for $$K_c$$?

Accepted Answer

$$K_c = 1 / ([\mathrm{Ru$$^{3+}$$}][\mathrm{Br^-}]^3)$$

Question 10

For the reaction $$2\ \mathrm{H_2O_2\ (aq)} \rightleftharpoons 2\ \mathrm{H_2O\ (l)} + \mathrm{O_2$\ (g)}$$, which of the following is the correct equilibrium expression for $$K_c$$?

Accepted Answer

$$K_c = [\mathrm{O_2$}] / [\mathrm{H_2O_2}]^2$$

Question 11

Consider the reaction $$\mathrm{H_2$\ (g)} + \mathrm{Br_2$\ (g)} ightleftharpoons 2\ \mathrm{HBr\ (g)}$$ with $$K_p = 2.1 	imes 10^2$. If the partial pressures are P$$_{\mathrm{$$H_2$$}} = 3.7\ \mathrm{atm}$$, P$$_{\mathrm{$$Br_2$$}} = 4.8\ \mathrm{atm}$$, and P$$_{\mathrm{HBr}} = 0.46\ \mathrm{atm}$$, what is the value of Q_c$ and in which direction will the reaction proceed?

Accepted Answer

$$Q_c = 0.012$$; reaction proceeds to the right (toward products)

Question 12

For the reaction $$\mathrm{NO_2$\ (g)} + \mathrm{N_2O\ (g)} ightleftharpoons 3\ \mathrm{NO\ (g)}$$ with $$K_c = 7.32 	imes 10$$^{-2}$$, if the initial concentrations are $$[\mathrm{$$NO_2$$}] = 1.33\ \mathrm{M}$$ and $$[\mathrm{N_2O}] = 1.84\ \mathrm{M}$$, and there is no NO initially, which of the following best describes the equilibrium concentrations?

Accepted Answer

The equilibrium concentration of NO will be much less than the initial concentrations of NO2 and N2O.

Question 13

If the reaction $$\mathrm{H_2$\ (g)} + \mathrm{F_2$\ (g)} \rightleftharpoons 2\ \mathrm{HF\ (g)}$$ ($$\Delta H = -537\ \mathrm{kJ}) is $$heated, in which direction will the equilibrium shift according to Le Chatelier's principle?

Accepted Answer

To the left (toward reactants)

Question 14

For the reaction $$2\ \mathrm{C\ (s)} + 2\ \mathrm{H_2$\ (g)} \rightleftharpoons \mathrm{C_2H_4\ (g)}$$ ($$\Delta H = +52.3\ \mathrm{kJ}$$), what will happen to the equilibrium position if the temperature is increased?

Accepted Answer

The equilibrium will shift to the right (toward products)

Question 15

If two reactions are added together, how is the equilibrium constant for the overall reaction ($$K_{c,3}) $$related to the equilibrium constants of the individual reactions ($$K_{c,1}$$ and $$K_{c,2}$$)?

Accepted Answer

$$K_{c,3} = K_{c,1} 	imes K_{c,2}$$

Question 16

A reaction mixture contains $$[\mathrm{H_2$}] = 3.7\ \mathrm{atm}$$, $$[\mathrm{Br_2$}] = 4.8\ \mathrm{atm}$$, and $$[\mathrm{HBr}] = 0.46\ \mathrm{atm}$$ for the reaction $$\mathrm{H_2$\ (g)} + \mathrm{Br_2$\ (g)} ightleftharpoons 2\ \mathrm{HBr\ (g)}. If$$ $$K_p = 2.1 	imes 10^2$, what does it mean if Q_c$$ \u003c K_p$$?

Accepted Answer

The reaction will proceed to the right to form more HBr.

Question 17

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

Accepted Answer

Their concentrations do not change during the reaction.

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