Q: Which of the following is the correct relationship between $$K_a$$ and $$K_b$$ for a conjugate acid-base pair in water at $$25^\circ\mathrm{C}$$?

$$K_a \times K_b = 1.0 \times 10$$^{-14}$$

Question 1

A reaction is found to be first order with respect to reactant A. If the initial concentration of A is $$0.80\ \mathrm{mol\ L$$^{-1}$$}$$ and after $$40\ \mathrm{min}$$ the concentration drops to $$0.20\ \mathrm{mol\ L$$^{-1}$$}$$, what is the rate constant $$k$$ for this reaction?

Accepted Answer

$$k = 0.0347\ \mathrm{min}^{-1}$$

Question 2

Which of the following statements best explains why increasing the temperature generally increases the rate of a chemical reaction?

Accepted Answer

It increases the number of collisions with sufficient energy to overcome the activation energy barrier.

Question 3

Given the reaction $$2\mathrm{NO}_2(g) \rightarrow 2\mathrm{NO}(g) + \mathrm{O}_2(g)$$, if the rate of disappearance of $$\mathrm{NO}_2 is$$ $$0.10\ \mathrm{mol\ L$$^{-1}$$\ s$$^{-1}$$}$$, what is the rate of appearance of $$\mathrm{O}_2$$?

Accepted Answer

$$0.05\ \mathrm{mol\ L$$^{-1}$$\ s$$^{-1}$$}$$

Question 4

A reaction mechanism consists of the following steps:

Step 1 (slow): $$A + B \rightarrow C$$

Step 2 (fast): $$C + D \rightarrow E$$

What is the rate law for the overall reaction?

Accepted Answer

Rate $$= k[A][B]$$

Question 5

For the equilibrium $$\mathrm{N}_2(g) + 3\mathrm{H}_2(g) \rightleftharpoons 2\mathrm{NH}_3(g)$$, which of the following changes will increase the amount of $$\mathrm{NH}_3 at $$equilibrium?

Accepted Answer

Increasing the pressure by decreasing the volume

Question 6

A solution has $$[H^+] = 3.2 	imes 10$$^{-5}$$\ \mathrm{M}. $$What is the pH of the solution?

Accepted Answer

pH $$= 4.49$$

Question 7

Which of the following is a correct equilibrium expression for the reaction $$\mathrm{CaCO}_3(s) \rightleftharpoons \mathrm{Ca}^{2+}(aq) + \mathrm{CO}_3$$^{2-}$$(aq)$$?

Accepted Answer

$$K_c = [\mathrm{Ca}^{2+}][\mathrm{CO}_3$$^{2-}$$]$$

Question 8

A weak acid, HA, has $$K_a = 1.8 	imes 10$$^{-5}$$. If 0.10$$\ \mathrm{mol}$$ of HA is dissolved in 1.0$$\ \mathrm{L}$$ of water, what is the pH of the solution? (Assume x$$ \ll 0.10$$)

Accepted Answer

pH $$= 2.37$$

Question 9

Which of the following statements about catalysts is TRUE?

Accepted Answer

A catalyst lowers the activation energy for both the forward and reverse reactions.

Question 10

For the reaction $$2\mathrm{SO}_2(g) + \mathrm{O}_2(g) \rightleftharpoons 2\mathrm{SO}_3(g)$$, $$K_p = 2.5. If $$the initial partial pressures are $$P_{SO_2$} = 0.50\ \mathrm{atm}$$, $$P_{O_2$} = 0.50\ \mathrm{atm}$$, and $$P_{SO_3$} = 0.10\ \mathrm{atm}$$, what is the value of the reaction quotient $$Q_p$$ and in which direction will the reaction proceed to reach equilibrium?

Accepted Answer

$$Q_p = 0.08$$, reaction proceeds to the right

Question 11

Which of the following salts will produce a basic solution when dissolved in water?

Accepted Answer

$$\mathrm{KCH}_3\mathrm{COO}$$

Question 12

Which of the following is the correct relationship between $$K_a$$ and $$K_b$$ for a conjugate acid-base pair in water at $$25^\circ\mathrm{C}$$?

Accepted Answer

$$K_a 	imes K_b = 1.0 	imes 10$$^{-14}$$

Question 13

Which of the following best describes a Lewis acid?

Accepted Answer

A substance that accepts an electron pair

Question 14

The half-life for a first-order reaction is $$20\ \mathrm{min}. $$How long will it take for the concentration of the reactant to decrease to $$12.5\% of $$its original value?

Accepted Answer

$$80\ \mathrm{min}$$

Question 15

Which of the following changes will NOT affect the position of equilibrium for the reaction $$\mathrm{H}_2(g) + \mathrm{I}_2(g) \rightleftharpoons 2\mathrm{HI}(g)$$?

Accepted Answer

Adding a catalyst

Question 16

Which of the following is the correct expression for the autoionization of water?

Accepted Answer

$$K_w = [H^+][OH^-]$$

Question 17

Which of the following best explains why $$\mathrm{HF} is a $$weak acid while $$\mathrm{HCl} is a $$strong acid?

Accepted Answer

$$\mathrm{HF}$$ has a stronger H--F bond and lower polarity compared to $$\mathrm{HCl}.$$

Question 18

A reaction has a rate law: Rate $$= k[A]^2[B]. If $$the concentration of $$A is $$doubled and $$B is $$halved, by what factor does the rate change?

Accepted Answer

The rate increases by a factor of 2

Question 19

Which of the following is a conjugate acid-base pair according to the Bronsted-Lowry definition?

Accepted Answer

$$\mathrm{NH}_4^+$$ / $$\mathrm{NH}_3$$

General Chemistry Study Guide: Chemical Kinetics, Chemical Equilibrium, and Acids & Bases (Chapters 15–17)

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