Q: A reaction has the rate equation $$\text{Rate} = k[A]^2[B]. If $$the initial rate is $$0.10\ \mathrm{mol\ L$$^{-1}$$\ s$$^{-1}$$}$$ when $$[A] = 0.5\ \mathrm{mol\ L$$^{-1}$$}$$ and $$[B] = 1.0\ \mathrm{mol\ L$$^{-1}$$}$$, what is the value of $$k$$?

$$0.10 \div (0.5^2$ \times 1.0) = 0.40$$

Question 1

Which of the following best describes the rate-determining step in a multi-step chemical reaction?

Accepted Answer

It is the step with the highest activation energy and controls the overall reaction rate.

Question 2

Given the rate equation $$	ext{Rate} = k[A]^2[B]$$, what is the overall order of the reaction?

Accepted Answer

$$3$$

Question 3

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

Accepted Answer

$$2 	imes 3^2$ = 18$$

Question 4

Which of the following statements about the rate constant $$k is $$correct?

Accepted Answer

$$k is $$only affected by temperature.

Question 5

In a reaction, doubling the concentration of reactant $$A$$ causes the rate to quadruple, while doubling $$B$$ has no effect. What is the most likely rate equation?

Accepted Answer

$$	ext{Rate} = k[A]^2$$

Question 6

Which of the following is NOT a factor that affects the rate of a chemical reaction?

Accepted Answer

The color of the reactants

Question 7

For the reaction $$	ext{Rate} = k[A]^0[B]^1$$, what is the order with respect to $$A$$ and what does this imply?

Accepted Answer

Order with respect to $$A is$$ $$0$$; rate is independent of $$[A].$$

Question 8

A student finds that the units of the rate constant $$k$$ for a reaction are $$\mathrm{$$mol^{-2}$$ \cdot L^2$ \cdot s$$^{-1}$$}. $$What is the overall order of the reaction?

Accepted Answer

$$3$$

Question 9

In a real-world scenario, the decomposition of hydrogen peroxide is catalyzed by manganese dioxide. Which statement best explains the effect of the catalyst on the rate equation?

Accepted Answer

The catalyst increases the value of $$k by $$providing an alternative pathway with lower activation energy.

Question 10

Experimental data for a reaction shows that when $$[A] is $$doubled, the rate increases by a factor of $$4$$, and when $$[B] is $$doubled, the rate doubles. What is the correct rate equation?

Accepted Answer

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

Question 11

Which of the following best explains why the slowest step in a reaction mechanism determines the overall rate?

Accepted Answer

Because no subsequent step can proceed faster than the slowest step.

Question 12

A reaction has the rate equation $$	ext{Rate} = k[A]^1[B]^0. If $$the concentration of $$A is $$halved and $$B is $$doubled, what happens to the rate?

Accepted Answer

The rate is halved.

Question 13

Which of the following is the correct definition of the rate constant $$k$$?

Accepted Answer

A proportionality constant in the rate equation that is only affected by temperature.

Question 14

In a laboratory experiment, a student observes that changing the concentration of $$B$$ does not affect the rate, but changing $$A$$ does. Which is the most likely order with respect to $$B$$?

Accepted Answer

Zero order

Question 15

A reaction has the rate equation $$	ext{Rate} = k[A]^2[B]. If $$the initial rate is $$0.10\ \mathrm{mol\ L$$^{-1}$$\ s$$^{-1}$$}$$ when $$[A] = 0.5\ \mathrm{mol\ L$$^{-1}$$}$$ and $$[B] = 1.0\ \mathrm{mol\ L$$^{-1}$$}$$, what is the value of $$k$$?

Accepted Answer

$$0.10 \div (0.5^2$ 	imes 1.0) = 0.40$$

Question 16

Which of the following best describes a zero-order reaction with respect to reactant $$A$$?

Accepted Answer

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

Question 17

A pharmaceutical company is testing a new drug that decomposes in the body according to the rate equation $$	ext{Rate} = k[D]^1. If $$the initial concentration of the drug is $$2.0\ \mathrm{mol\ L$$^{-1}$$}$$ and the rate constant $$k = 0.5\ \mathrm{h$$^{-1}$$}$$, what is the initial rate of decomposition?

Accepted Answer

$$1.0\ \mathrm{mol\ L$$^{-1}$$\ h$$^{-1}$$}$$

Question 18

If a reaction is first order with respect to $$A$$ and zero order with respect to $$B$$, which of the following graphs would yield a straight line?

Accepted Answer

A plot of rate vs. $$[A]$$

Question 19

Which of the following best explains why the units of the rate constant $$k$$ change depending on the overall order of the reaction?

Accepted Answer

Because the units of rate and concentration must balance in the rate equation.

Rate Equations and Reaction Mechanisms: Study Notes

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