Q: Given the reaction $$2A \rightleftharpoons B$$ with equilibrium constant $$K_1$$, and $$B \rightleftharpoons C$$ with equilibrium constant $$K_2$$, what is the overall equilibrium constant $$K_{\text{overall}}$$ for $$2A \rightleftharpoons C$$?

$$K_{\text{overall}} = K_1$ \cdot K_2$

Question 1

Which of the following best describes what happens to the concentrations of reactants and products as a chemical reaction approaches equilibrium, as shown in the concentration vs. time graph?

Accepted Answer

The concentrations of reactants decrease and products increase until they become constant at equilibrium.

Question 2

For the reaction $$\mathrm{$$PCl_5$$ \rightleftharpoons $$PCl_3$$ + Cl_2$}$$, if the initial concentration of $$\mathrm{$$PCl_5$$} is$$ $$1.00\ M$$ and the equilibrium constant $$K_c is$$ $$0.0211$$, what is the equilibrium concentration of $$\mathrm{Cl_2$}$$?

Accepted Answer

$$0.135\ M$$

Question 3

Given the reaction $$2A ightleftharpoons B$$ with equilibrium constant $$K_1$$, and $$B ightleftharpoons C$$ with equilibrium constant $$K_2$$, what is the overall equilibrium constant $$K_{	ext{overall}}$$ for $$2A ightleftharpoons C$$?

Accepted Answer

$$K_{	ext{overall}} = K_1$ \cdot K_2$

Question 4

If the equilibrium constant for $$A \rightleftharpoons B is$$ $$K$$, what is the equilibrium constant for $$B \rightleftharpoons A$$?

Accepted Answer

$$1/K$$

Question 5

A reaction mixture initially contains only reactants. As the reaction proceeds, the value of the reaction quotient $$Q$$ changes. When $$Q \u003c K$$, what will happen to the system?

Accepted Answer

The reaction will shift to the right to form more products.

Question 6

For the reaction $$\mathrm{$$COCl_2$$(g) \rightleftharpoons CO(g) + Cl_2$(g)}$$, what will happen if the volume of the container is doubled at constant temperature?

Accepted Answer

The reaction will shift to the right, favoring the formation of $$\mathrm{CO}$$ and $$\mathrm{Cl_2$}.$$

Question 7

Which of the following statements about a catalyst in a chemical reaction is correct?

Accepted Answer

A catalyst decreases the activation energy and speeds up the attainment of equilibrium.

Question 8

For the reaction $$A \rightleftharpoons B$$, if the equilibrium constant $$K is $$expressed as $$K = \frac{[B]}{[A]}$$, what is the value of $$K'$$ for the reaction $$2A \rightleftharpoons 2B$$?

Accepted Answer

$$K' = K^2$

Question 9

A student is solving for the equilibrium concentration of $$\mathrm{H_3O^+} in a $$weak acid solution using the quadratic formula. Which equation should they use if their ICE table gives $$x^2 + 0.0211x - 0.0211 = 0$?

Accepted Answer

$$x = \frac{-0.0211 \pm \sqrt{(0.0211)^2$ - 4(1)(-0.0211)}}{2(1)}$$

Question 10

In a reaction at equilibrium, what happens to the rates of the forward and reverse reactions?

Accepted Answer

The rates of the forward and reverse reactions are equal.

Question 11

For the reaction $$\mathrm{HCO_2H(aq) + H_2O(l) ightleftharpoons H_3O^+(aq) + CO_2H^-(aq)}$$ with $$K_a = 1.8 	imes 10$$^{-4}$$ and initial $$[\mathrm{HCO_2H}] = 0.250\ M$$, what simplifying assumption can be made to solve for $$[\mathrm{H_3O^+}]$$ at equilibrium?

Accepted Answer

Assume $$x is $$much smaller than $$0.250$$

Question 12

If the reaction quotient $$Q is $$greater than the equilibrium constant $$K$$ for a gaseous reaction, what will happen to the system?

Accepted Answer

The reaction will shift to the left to form more reactants.

Question 13

Which of the following best explains why only the positive root of the quadratic equation is used to determine equilibrium concentrations in chemical systems?

Accepted Answer

Negative concentrations are not physically meaningful.

Question 14

A reaction has $$\Delta n \u003c 0 ($$fewer moles of gas on the product side). What will happen if the volume of the reaction vessel is decreased?

Accepted Answer

The reaction will shift to the left.

Question 15

Which of the following is the correct equilibrium constant expression for the reaction $$2A \rightleftharpoons B$$?

Accepted Answer

$$K = \frac{[B]}{[A]^2}$$

Question 16

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 favors reactants at equilibrium.

Question 17

A real-world application: In the industrial synthesis of ammonia ($$\mathrm{N_2$ + 3H_2 \rightleftharpoons 2NH_3}$$), what would be the effect of increasing the pressure on the equilibrium position?

Accepted Answer

The equilibrium will shift to produce more $$\mathrm{NH_3$}.$$

Principles of Chemical Equilibrium: Concepts, Calculations, and Applications

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