Q: The decomposition of ammonia on a tungsten surface at $$1100\ ^\circ\mathrm{C}$$ follows the reaction $$NH_3$$ \rightarrow \frac{1}{2}$$N_2$$ + \frac{3}{2}$$H_2. In an $$experiment, the initial concentration of $$NH_3$$ was $$3.72 \times 10$$^{-4}$$\ \mathrm{M}$$ and dropped to $$3.98 \times 10$$^{-4}$$\ \mathrm{M}$$ after $$614$$ seconds. What is the average rate of disappearance of $$NH_3$$?

$$-4.23 \times 10$$^{-7}$$\ \mathrm{M\ s$$^{-1}$$}$$

Question 1

For the reaction $$2NO_2(g) \rightarrow N_2O_4(g)$$, if the rate of appearance of $$N_2O_4 is$$ $$0.300\ \mathrm{M\ s$$^{-1}$$}$$, what is the rate of disappearance of $$NO_2$$?

Accepted Answer

$$0.600\ \mathrm{M\ s$$^{-1}$$}$$

Question 2

Given the rate law $$	ext{rate} = k[NO_2$][O_2$]$$, what is the overall order of the reaction?

Accepted Answer

Second order

Question 3

A reaction follows the rate law $$	ext{rate} = k[A]^2[B]. If$$ $$	ext{rate} = 2.50\ \mathrm{M\ s$$^{-1}$$}$$ when $$[A] = 0.5000\ \mathrm{M}$$ and $$[B] = 0.5000\ \mathrm{M}$$, what is the value of the rate constant $$k$$?

Accepted Answer

$$k = 20.0\ \mathrm{M$$^{-2}$$\ s$$^{-1}$$}$$

Question 4

The decomposition of ammonia on a tungsten surface at $$1100\ ^\circ\mathrm{C}$$ follows the reaction $$NH_3$$ ightarrow \frac{1}{2}$$N_2$$ + \frac{3}{2}$$H_2. In an $$experiment, the initial concentration of $$NH_3$$ was $$3.72 	imes 10$$^{-4}$$\ \mathrm{M}$$ and dropped to $$3.98 	imes 10$$^{-4}$$\ \mathrm{M}$$ after $$614$$ seconds. What is the average rate of disappearance of $$NH_3$$?

Accepted Answer

$$-4.23 	imes 10$$^{-7}$$\ \mathrm{M\ s$$^{-1}$$}$$

Question 5

For the reaction $$2A + 2B ightarrow C$$, the following initial rates were measured:

$$[A] = 0.10\ \mathrm{M}, [B] = 0.10\ \mathrm{M}, 	ext{rate} = 0.020$$
$$[A] = 0.20\ \mathrm{M}, [B] = 0.10\ \mathrm{M}, 	ext{rate} = 0.080$$
$$[A] = 0.10\ \mathrm{M}, [B] = 0.30\ \mathrm{M}, 	ext{rate} = 0.060$$

What is the rate law for this reaction?

Accepted Answer

$$	ext{rate} = k[A]^2[B]^1$$

Question 6

Which of the following is the correct integrated rate law for a first-order reaction?

Accepted Answer

$$\ln[A]_t = -kt + \ln[A]_0$$

Question 7

A reaction has a rate constant $$k = 0.132\ \mathrm{M$$^{-1}$$\ s$$^{-1}$$}. $$What is the order of the reaction?

Accepted Answer

Second order

Question 8

The decomposition of nitramide, $$NH_2NO_2$$, at $$25^\circC is $$first order with $$k = 4.70 	imes 10$$^{-5}$$\ \mathrm{s$$^{-1}$$}. If $$the initial concentration is $$0.774\ \mathrm{M}$$, what is the concentration after $$34500$$ seconds?

Accepted Answer

$$0.200\ \mathrm{M}$$

Question 9

Which of the following correctly expresses the half-life for a first-order reaction?

Accepted Answer

$$t_{1/2} = \frac{\ln 2}{k}$$

Question 10

A pesticide in a lake decomposes with a half-life of $$10.2$$ years. If the present concentration is $$0.0500\ \mathrm{mg/L}$$, what was its concentration $$4$$ years ago? (Assume first-order kinetics.)

Accepted Answer

$$0.0600\ \mathrm{mg/L}$$

Question 11

Which of the following statements about the Arrhenius equation is correct?

Accepted Answer

The rate constant $$k$$ increases as temperature increases.

Question 12

For a reaction with the rate law $$	ext{rate} = k[A]$$, which of the following plots will yield a straight line?

Accepted Answer

$$\ln[A] vs. $$time

Question 13

A reaction is found to be zero order in $$[A]. $$Which of the following is true about the rate of the reaction?

Accepted Answer

The rate is independent of $$[A].$$

Question 14

If a reaction has the rate law $$	ext{rate} = k[A]^2$$, what are the units of the rate constant $$k$$?

Accepted Answer

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

Question 15

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

Accepted Answer

It decreases the activation energy.

Question 16

A student measures the rate of a reaction at several different temperatures and finds that the rate constant doubles when the temperature increases by $$10^\circC. $$What does this suggest about the activation energy?

Accepted Answer

The activation energy is moderate to high.

Question 17

For a second-order reaction, which of the following is the correct integrated rate law?

Accepted Answer

$$\frac{1}{[A]_t} = kt + \frac{1}{[A]_0}$$

Question 18

Which of the following is a correct statement about the rate-determining step in a reaction mechanism?

Accepted Answer

It is the slowest step in the mechanism.

Question 19

A reaction has a rate law $$	ext{rate} = k[A][B]^2. If $$the concentration of $$A is $$doubled and $$B is $$tripled, by what factor does the rate increase?

Accepted Answer

18

Chapter 12: Chemical Kinetics – Study Notes

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