Q: Consider the reaction $$\mathrm{N}_2(g) + 3\,\mathrm{H}_2(g) \rightleftharpoons 2\,\mathrm{NH}_3(g). If $$the equilibrium constant $$K_c is$$ $$0.50 at a $$certain temperature, what is the value of $$K_p at$$ $$400\,\mathrm{K}$$? ($$R = 0.08206\,\mathrm{L}\,\mathrm{atm}/(\mathrm{mol}\,\mathrm{K}))$$

$$K_p = K_c \times (RT$$)^{-2}$$ = 0.50 \times (0.08206 \times 400$$)^{-2}$$ \approx 0.0012$$

Question 1

A reaction is found to be first order with respect to reactant A. If the initial concentration of A is doubled, how does the rate of the reaction change?

Accepted Answer

The rate increases by a factor of 2.

Question 2

Which of the following best describes the effect of a catalyst on a chemical reaction?

Accepted Answer

It lowers the activation energy, providing an alternative pathway for the reaction.

Question 3

For the reaction $$2\,\mathrm{NO}_2(g) ightarrow 2\,\mathrm{NO}(g) + \mathrm{O}_2(g)$$, the rate law is found to be $$	ext{rate} = k[\mathrm{NO}_2]^2. If $$the initial concentration of $$\mathrm{NO}_2 is$$ $$0.10\,\mathrm{M}$$ and the rate constant $$k = 0.54\,\mathrm{M}^{-1}\mathrm{s}^{-1}$$, what is the initial rate?

Accepted Answer

$$0.0054\,\mathrm{M}\,\mathrm{s}^{-1}$$

Question 4

Which of the following statements about chemical equilibrium is correct?

Accepted Answer

At equilibrium, the rates of the forward and reverse reactions are equal.

Question 5

Consider the reaction $$\mathrm{N}_2(g) + 3\,\mathrm{H}_2(g) \rightleftharpoons 2\,\mathrm{NH}_3(g). If $$the equilibrium constant $$K_c is$$ $$0.50 at a $$certain temperature, what is the value of $$K_p at$$ $$400\,\mathrm{K}$$? ($$R = 0.08206\,\mathrm{L}\,\mathrm{atm}/(\mathrm{mol}\,\mathrm{K}))$$

Accepted Answer

$$K_p = K_c 	imes (RT$$)^{-2}$$ = 0.50 	imes (0.08206 	imes 400$$)^{-2}$$ \approx 0.0012$$

Question 6

A weak acid, HA, has a $$K_a of$$ $$1.8 	imes 10$$^{-5}$$. What is the pH of a 0.10$$\,\mathrm{M}$$ solution of HA? (Assume the 5% approximation is valid.)

Accepted Answer

pH $$= 2.87$$

Question 7

Which of the following changes will shift the equilibrium to the right for the exothermic reaction $$\mathrm{N}_2(g) + 3\,\mathrm{H}_2(g) ightleftharpoons 2\,\mathrm{NH}_3(g) + 	ext{heat}$$?

Accepted Answer

Increasing the pressure by decreasing the volume.

Question 8

The half-life for a first-order reaction is given by which equation?

Accepted Answer

$$t_{1/2} = \dfrac{0.693}{k}$$

Question 9

A solution has $$[\mathrm{H}^+] = 3.2 	imes 10$$^{-4}$$\,\mathrm{M}. $$What is the pH of the solution?

Accepted Answer

pH $$= 3.49$$

Question 10

Which of the following statements is true regarding the relationship between $$K$$ and $$Q$$ for a chemical reaction?

Accepted Answer

If $$Q \u003c K$$, the reaction will proceed in the forward direction to reach equilibrium.

Question 11

Which of the following acids is expected to be the strongest, based on bond strength and electronegativity?

Accepted Answer

HI

Question 12

A $$0.020\,\mathrm{M}$$ solution of a weak base, $$B$$, has a pH of $$10.80. $$What is the value of $$K_b$$ for this base?

Accepted Answer

$$K_b = 2.5 	imes 10$$^{-5}$$

Question 13

Which of the following best describes the effect of increasing temperature on the rate constant $$k$$ for a reaction, according to the Arrhenius equation?

Accepted Answer

Increasing temperature increases $$k$$ because more molecules have energy greater than the activation energy.

Question 14

A reaction has an activation energy of $$75\,\mathrm{kJ}/\mathrm{mol}. If $$the temperature is increased from $$300\,\mathrm{K} to$$ $$310\,\mathrm{K}$$, what happens to the rate constant $$k$$?

Accepted Answer

The rate constant increases.

Question 15

Which of the following is true for the equilibrium constant $$K$$ for a reaction involving only solids and liquids?

Accepted Answer

The concentrations of pure solids and liquids are omitted from the expression for $$K.$$

Question 16

A $$0.10\,\mathrm{M}$$ solution of a diprotic acid, $$H_2A$$, has $$K_{a1} = 1.0 	imes 10$$^{-3}$$ and K$$_{a2} = 1.0 	imes $$10^{-7}. $$What is the pH of the solution?

Accepted Answer

pH $$= 2.0$$

Question 17

Which of the following is the correct expression for the equilibrium constant $$K_c$$ for the reaction $$\mathrm{CO}(g) + 2\,\mathrm{H}_2(g) \rightleftharpoons \mathrm{CH}_3\mathrm{OH}(g)$$?

Accepted Answer

$$K_c = \dfrac{[\mathrm{CH}_3\mathrm{OH}]}{[\mathrm{CO}][\mathrm{H}_2]^2}$$

Question 18

If the rate law for a reaction is $$	ext{rate} = k[A][B]^2$$, what is the overall order of the reaction?

Accepted Answer

Third order

Question 19

A $$0.050\,\mathrm{M}$$ solution of a weak acid has a pH of $$3.00. $$What is the value of $$K_a$$ for this acid?

Accepted Answer

$$K_a = 1.0 	imes 10$$^{-4}$$

General Chemistry Study Guide: Chemical Kinetics, Chemical Equilibrium, and Acid-Base Equilibria

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