Question 1

Which of the following best describes the dynamic nature of chemical equilibrium in a closed system?

Accepted Answer

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

Question 2

Consider the decomposition of calcium carbonate in cement production: $$\mathrm{$$CaCO_3$$(s) \rightarrow CaO(s) + CO_2$(g)}. $$What is the correct equilibrium constant expression for this reaction?

Accepted Answer

$$K = [\mathrm{CO_2$}]$$

Question 3

A mixture of $$0.050\ \mathrm{M}$$ hydrogen gas and $$0.050\ \mathrm{M}$$ iodine gas is allowed to reach equilibrium at a temperature where $$K = 59.3$$ for the reaction $$\mathrm{H_2$(g) + I_2$(g) \rightleftharpoons 2HI(g)}. $$What is the equilibrium concentration of $$\mathrm{HI}$$?

Accepted Answer

$$0.077\ \mathrm{M}$$

Question 4

Which of the following changes will shift the equilibrium to the right for the reaction $$\mathrm{CH_3COOH(aq) \rightleftharpoons H^+(aq) + CH_3COO^-(aq)}$$?

Accepted Answer

Adding more acetic acid

Question 5

For the reaction $$\mathrm{2SO_2(g) + O_2$(g) \rightleftharpoons 2SO_3(g)}$$, what will happen to the equilibrium position if the pressure is increased?

Accepted Answer

It will shift to the right, favoring the formation of $$\mathrm{SO_3$}.$$

Question 6

Which statement correctly describes the effect of a catalyst on a system at equilibrium?

Accepted Answer

A catalyst speeds up both the forward and reverse reactions equally, but does not change the equilibrium concentrations.

Question 7

Given the reaction $$\mathrm{N_2$(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)}$$, what is the equilibrium constant expression?

Accepted Answer

$$K = \frac{[\mathrm{NH_3$}]^2}{[\mathrm{N_2$}][\mathrm{H_2$}]^3}$$

Question 8

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

Accepted Answer

The reactants are favored at equilibrium.

Question 9

For the precipitation reaction $$\mathrm{Ca$$^{2+}$$(aq) + 2OH^-(aq) \rightleftharpoons Ca(OH)_2(s)}$$, what is the correct equilibrium constant expression?

Accepted Answer

$$K = \frac{1}{[\mathrm{Ca$$^{2+}$$}][\mathrm{OH^-}]^2}$$

Question 10

Which of the following best explains why the concentration of a pure solid or liquid is not included in the equilibrium constant expression?

Accepted Answer

Their concentrations are constant and do not affect the equilibrium position.

Question 11

If the reaction $$\mathrm{A + B \rightleftharpoons C + D}$$ has an equilibrium constant $$K$$, what is the equilibrium constant for the reverse reaction $$\mathrm{C + D \rightleftharpoons A + B}$$?

Accepted Answer

$$1/K$$

Question 12

A system at equilibrium is disturbed by increasing the temperature of an exothermic reaction. What is the expected effect on the equilibrium position?

Accepted Answer

The equilibrium shifts toward the reactants.

Question 13

Which of the following statements about Le Chatelier’s Principle is correct?

Accepted Answer

A system at equilibrium will always shift to oppose any applied stress.

Question 14

For the reaction $$\mathrm{2NO_2(g) \rightleftharpoons N_2O_4(g)}$$, what will happen if the volume of the container is decreased?

Accepted Answer

The equilibrium will shift to the right, favoring $$\mathrm{N_2O_4}.$$

Question 15

Which of the following is true regarding the relationship between $$K_c$$ and $$K_p$$ for a gaseous reaction?

Accepted Answer

$$K_p = K_c 	imes (RT$$)^{\Delta n}$$, where $$\Delta n$$ is the change in moles of gas.

Question 16

A reaction has a standard free energy change $$\Delta G^\circ = -40\ \mathrm{kJ\ $$mol^{-1}$$} at$$ $$298\ \mathrm{K}. $$What can be said about the equilibrium constant $$K$$ for this reaction?

Accepted Answer

$$K is $$much greater than 1.

Question 17

Which of the following real-world scenarios is an example of a heterogeneous equilibrium?

Accepted Answer

The decomposition of $$\mathrm{$$CaCO_3$$(s)} to$$ $$\mathrm{CaO(s)}$$ and $$\mathrm{CO_2$(g)}$$

Question 18

If two reactions are added together, how is the equilibrium constant for the overall reaction related to the equilibrium constants of the individual reactions?

Accepted Answer

It is the product of the individual equilibrium constants.

Question 19

Which of the following best explains why fly ash is used as a partial replacement for Portland cement in concrete?

Accepted Answer

Fly ash consists of small spherical particles that improve the strength and durability of concrete.

Question 20

Which of the following would increase the solubility of $$\mathrm{Ca(OH)_2} in $$water?

Accepted Answer

Removing $$\mathrm{OH^-}$$ ions.

Chemical Equilibrium: Applications in Concrete Production and Weathering

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