Question 1

Which of the following best describes the role of activation energy in a chemical reaction, as shown in the energy diagram for the reaction $$2\ \mathrm{H}_2(g) + \mathrm{O}_2(g) \rightarrow 2\ \mathrm{H}_2\mathrm{O}(g)$$?

Accepted Answer

It is the minimum energy required for reactants to transform into products.

Question 2

For a first-order reaction, which of the following plots yields a straight line, and what is the slope of that line?

Accepted Answer

A plot of $$\ln [A]_t vs$$. $$t$$ with a slope of $$-k.$$

Question 3

A reaction is found to have a rate law: $$	ext{rate} = k[A]^2. If $$the initial concentration of $$A is $$doubled, how does the initial rate change?

Accepted Answer

It quadruples.

Question 4

The half-life of a first-order reaction is given by $$t_{1/2} = \frac{\ln 2}{k}. $$Which statement is true about the half-life of a first-order reaction?

Accepted Answer

It is constant and independent of the initial concentration.

Question 5

Given the Arrhenius equation $$k = A e$$^{-E_a/(RT)}$$, what effect does increasing the temperature have on the rate constant k$?

Accepted Answer

It increases $$k.$$

Question 6

A zero-order reaction has an initial concentration $$[A]_0 = 0.50\ \mathrm{M}$$ and a rate constant $$k = 0.10\ \mathrm{M/s}. $$How long will it take for the concentration to decrease to $$0.20\ \mathrm{M}$$?

Accepted Answer

$$3.0\ \mathrm{s}$$

Question 7

Which of the following is true for a second-order reaction with respect to $$A$$?

Accepted Answer

A plot of $$1/[A]_t vs$$. $$t is $$linear.

Question 8

The isomerization of cyclopropane to propene is a first-order reaction with $$k = 3.36 	imes 10$$^{-5}$$\ \mathrm{s}^{-1} at$$ $$720\ \mathrm{K}. If $$the initial concentration is $$0.0445\ \mathrm{M}$$, what is the concentration after $$235.0$$ minutes?

Accepted Answer

$$0.00277\ \mathrm{M}$$

Question 9

Which of the following statements about the transition state (activated complex) is correct?

Accepted Answer

It has the highest energy along the reaction pathway.

Question 10

For a reaction with the rate law $$	ext{rate} = k[A]$$, what is the integrated rate law?

Accepted Answer

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

Question 11

A reaction has a rate constant $$k_1 at $$temperature $$T_1$$ and $$k_2 at $$temperature $$T_2. $$Which equation allows you to calculate the activation energy $$E_a$$ using these values?

Accepted Answer

$$\ln \left(\frac{k_2$}{k_1$}\right) = \frac{E_a}{R} \left(\frac{1}{T_1$} - \frac{1}{T_2$}\right)$$

Question 12

Which of the following factors does NOT affect the rate constant $$k in $$the Arrhenius equation?

Accepted Answer

Concentration of reactants

Question 13

A first-order reaction has a half-life of $$10$$ minutes. How much time is required for the concentration to decrease to $$1/8 of $$its initial value?

Accepted Answer

$$30$$ minutes

Question 14

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

Accepted Answer

It increases the number of molecules with energy greater than the activation energy.

Question 15

For a zero-order reaction, which of the following is true about the rate of reaction as the concentration of reactant decreases?

Accepted Answer

The rate remains constant.

Question 16

A reaction has a rate law $$	ext{rate} = k[A]. If $$the rate constant $$k is$$ $$0.020\ \mathrm{s}^{-1}$$, what is the half-life of the reaction?

Accepted Answer

$$13.9\ \mathrm{s}$$

Question 17

Which of the following statements about the frequency factor $$A in $$the Arrhenius equation is correct?

Accepted Answer

It is related to the number of effective collisions and molecular orientation.

Question 18

In a real-world scenario, why might a reaction with a large negative $$\Delta H ($$exothermic) still proceed very slowly at room temperature?

Accepted Answer

Because the activation energy is very high.

Chemical Kinetics II: Rate Laws, Integrated Rate Laws, and Activation Energy

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