Q: Given the following reactions and their equilibrium constants at a certain temperature: $$\mathrm{A(g) \rightleftharpoons 2B(g)} \quad K_1$ = 4$$ $$\mathrm{B(g) \rightleftharpoons C(g)} \quad K_2$ = 3$$ What is the equilibrium constant for the reaction $$\mathrm{A(g) \rightleftharpoons 2C(g)}$$?

$$K = K_1$ \times K_2$^2 = 4 \times 9 = 36$$

Q: A reaction mixture has $$[A] = 0.20\,\mathrm{M}$$, $$[B] = 0.10\,\mathrm{M}$$, and $$[C] = 0.40\,\mathrm{M}$$ for the reaction $$\mathrm{A + 2B \rightleftharpoons C}. If$$ $$K_c = 10$$, what is the value of the reaction quotient $$Q$$ and in which direction will the reaction proceed to reach equilibrium?

$$Q = \frac{[C]}{[A][B]^2} = \frac{0.40}{0.20 \times (0.10)^2$} = 200$$; reaction proceeds to the left.

Question 1

Which of the following best describes a system at chemical equilibrium?

Accepted Answer

The rates of the forward and reverse reactions are equal, and the concentrations of reactants and products remain constant over time.

Question 2

For the reaction $$\mathrm{N_2O_4(g) \rightleftharpoons 2NO_2(g)}$$, the equilibrium constant expression is:

Accepted Answer

$$K = \frac{[NO_2$]^2}{[N_2O_4]}$$

Question 3

Consider the reaction $$\mathrm{2SO_2(g) + O_2$(g) \rightleftharpoons 2SO_3(g)}. If $$the equilibrium concentrations are $$[SO_2$] = 0.10\,M$$, $$[O_2$] = 0.20\,M$$, and $$[SO_3$] = 0.40\,M$$, what is the value of the equilibrium constant $$K_c$$?

Accepted Answer

$$K_c = \frac{[SO_3$]^2}{[SO_2$]^2[O_2$]} = \frac{(0.40)^2$}{(0.10)^2$ 	imes 0.20} = 80$$

Question 4

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

Accepted Answer

The reaction is reactant-favored; reactants predominate at equilibrium.

Question 5

For the reaction $$\mathrm{A(g) + 2B(g) \rightleftharpoons 3C(g)}$$, the equilibrium constant $$K_c is 10. $$What is the value of $$K_c$$ for the reverse reaction?

Accepted Answer

$$K_c = 0.1$$

Question 6

Which of the following statements about heterogeneous equilibria is correct?

Accepted Answer

The concentrations of pure solids and liquids are omitted from the equilibrium constant expression.

Question 7

Given the following reactions and their equilibrium constants at a certain temperature:

$$\mathrm{A(g) \rightleftharpoons 2B(g)} \quad K_1$ = 4$$

$$\mathrm{B(g) \rightleftharpoons C(g)} \quad K_2$ = 3$$

What is the equilibrium constant for the reaction $$\mathrm{A(g) \rightleftharpoons 2C(g)}$$?

Accepted Answer

$$K = K_1$ 	imes K_2$^2 = 4 	imes 9 = 36$$

Question 8

A closed system initially contains $$1.00\,\mathrm{mol} of$$ $$\mathrm{H_2$}$$ and $$2.00\,\mathrm{mol} of$$ $$\mathrm{I_2$} in a$$ $$2.00\,\mathrm{L}$$ container at $$448^\circ\mathrm{C}. $$The equilibrium constant for the reaction $$\mathrm{H_2$(g) + I_2$(g) \rightleftharpoons 2HI(g)} is$$ $$K_c = 51. If $$the equilibrium concentration of $$\mathrm{HI} is$$ $$1.87\,\mathrm{M}$$, what is the equilibrium concentration of $$\mathrm{H_2$}$$?

Accepted Answer

$$[H_2$] = 0.065\,\mathrm{M}$$

Question 9

For the reaction $$\mathrm{2NO_2(g) \rightleftharpoons N_2O_4(g)}$$, $$K_c = 0.212 at$$ $$100^\circ\mathrm{C}. $$What is the value of $$K_c$$ for the reaction $$\mathrm{N_2O_4(g) \rightleftharpoons 2NO_2(g)} at $$the same temperature?

Accepted Answer

$$K_c = 1/0.212 = 4.72$$

Question 10

Which of the following changes will shift the equilibrium to the right for the endothermic reaction $$\mathrm{A(g) + B(g) \rightleftharpoons C(g) + D(g)}$$?

Accepted Answer

Removing product D

Question 11

A reaction mixture has $$[A] = 0.20\,\mathrm{M}$$, $$[B] = 0.10\,\mathrm{M}$$, and $$[C] = 0.40\,\mathrm{M}$$ for the reaction $$\mathrm{A + 2B \rightleftharpoons C}. If$$ $$K_c = 10$$, what is the value of the reaction quotient $$Q$$ and in which direction will the reaction proceed to reach equilibrium?

Accepted Answer

$$Q = \frac{[C]}{[A][B]^2} = \frac{0.40}{0.20 	imes (0.10)^2$} = 200$$; reaction proceeds to the left.

Question 12

Which of the following statements about catalysts and equilibrium is correct?

Accepted Answer

A catalyst allows equilibrium to be reached faster but does not change the equilibrium composition.

Question 13

For the reaction $$\mathrm{$$CaCO_3$$(s) \rightleftharpoons CaO(s) + CO_2$(g)}$$, which of the following is the correct equilibrium constant expression?

Accepted Answer

$$K = [CO_2$]$$

Question 14

If the volume of a reaction vessel is decreased for the reaction $$\mathrm{2A(g) + B(g) \rightleftharpoons 3C(g)}$$, how will the equilibrium shift?

Accepted Answer

Toward the side with fewer moles of gas (reactants)

Question 15

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

Accepted Answer

Their concentrations are essentially constant at a given temperature.

Question 16

For the exothermic reaction $$\mathrm{A(g) + B(g) \rightleftharpoons C(g) + D(g)}$$, what will happen to the equilibrium position if the temperature is increased?

Accepted Answer

The equilibrium will shift to the left, favoring reactants.

Question 17

A $$1.00\,\mathrm{L}$$ flask is filled with $$1.00\,\mathrm{mol} of$$ $$\mathrm{H_2$}$$ and $$2.00\,\mathrm{mol} of$$ $$\mathrm{I_2$} at$$ $$448^\circ\mathrm{C}. $$The equilibrium constant for $$\mathrm{H_2$(g) + I_2$(g) \rightleftharpoons 2HI(g)} is$$ $$K_c = 50.5. $$What is the equilibrium concentration of $$\mathrm{HI} if$$ $$x is $$the change in $$\mathrm{H_2$}$$ and $$\mathrm{I_2$}$$ concentration?

Accepted Answer

$$[HI] = 2x$$

Question 18

Which of the following is true regarding the effect of increasing the concentration of a reactant in a system at equilibrium?

Accepted Answer

The equilibrium shifts to the right, producing more products.

Chapter 15: Chemical Equilibrium – Study Notes

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