Q: A reaction has a rate constant $$k = 0.00693\ \mathrm{s$$^{-1}$$}. If $$the initial concentration of $$\mathrm{N_2O_5} is$$ $$0.375\ \mathrm{M}$$, what is the concentration after 3 minutes (180 s) for a first-order reaction?

$$[\mathrm{N_2O_5}] = 0.375 e$$^{-0.00693 \times 180}$$ = 0.142\ \mathrm{M}$$

Q: For the reaction $$\mathrm{S_2O_8$$^{2-}$$}(aq) + 3\mathrm{I^-}(aq) \rightarrow 2\mathrm{SO_4$^{2-}}(aq) + \mathrm{I_3$^-}(aq)$$, if doubling $$[\mathrm{S_2O_8$$^{2-}$$}]$$ doubles the rate and doubling $$[\mathrm{I^-}]$$ also doubles the rate, what is the rate law?

$$\text{rate} = k[\mathrm{S_2O_8$$^{2-}$$}][\mathrm{I^-}]$$

Question 1

Which of the following best describes the collision model for chemical reactions, as illustrated in the first image (two A atoms and one B atom colliding)?

Accepted Answer

Reactions occur only when reactant particles collide with sufficient energy and proper orientation.

Question 2

Given the reaction $$\mathrm{H_2$(g) + I_2$(g) \rightarrow 2HI(g)}$$, as shown in the second image, which statement is correct about the concentration changes over time?

Accepted Answer

The concentration of HI increases while the concentration of H2 decreases.

Question 3

For the decomposition of dinitrogen pentoxide, $$2\mathrm{N_2O_5}(g) \rightarrow 2\mathrm{N_2O_4}(g) + \mathrm{O_2$}(g)$$, which integrated rate law would you use if the reaction is first order?

Accepted Answer

$$\ln [\mathrm{N_2O_5}] = -kt + \ln [\mathrm{N_2O_5}]_0$$

Question 4

Based on the data for the decomposition of $$\mathrm{C_4H_6} ($$see tables and graphs), what is the order of the reaction?

Accepted Answer

Second order

Question 5

Which graph would you expect to be linear for a second-order reaction with respect to $$\mathrm{C_4H_6}$$?

Accepted Answer

A plot of $$\frac{1}{[\mathrm{C_4H_6}]}$$ versus time

Question 6

For the reaction $$4\mathrm{NO}(g) + \mathrm{O_2$}(g) \rightarrow 2\mathrm{N_2O_3}(g)$$, if $$\mathrm{N_2O_3} is $$being formed at a rate of $$0.048\ \mathrm{M\ s$$^{-1}$$}$$, what is the rate of disappearance of $$\mathrm{NO}$$?

Accepted Answer

$$0.096\ \mathrm{M\ s$$^{-1}$$}$$

Question 7

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

Accepted Answer

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

Question 8

If the rate law for a reaction is $$	ext{rate} = k[\mathrm{NO}]^2[\mathrm{H_2$}]$$, what is the overall order of the reaction?

Accepted Answer

Third order

Question 9

For the reaction $$2\mathrm{NO}(g) + 2\mathrm{H_2$}(g) ightarrow \mathrm{N_2$}(g) + 2\mathrm{H_2O}(g)$$, if the rate law is $$	ext{rate} = k[\mathrm{NO}]^2[\mathrm{H_2$}]$$, what happens to the rate if $$[\mathrm{NO}] is $$doubled and $$[\mathrm{H_2$}] is $$kept constant?

Accepted Answer

The rate increases by a factor of 4.

Question 10

A reaction has a rate constant $$k = 0.00693\ \mathrm{s$$^{-1}$$}. If $$the initial concentration of $$\mathrm{N_2O_5} is$$ $$0.375\ \mathrm{M}$$, what is the concentration after 3 minutes (180 s) for a first-order reaction?

Accepted Answer

$$[\mathrm{N_2O_5}] = 0.375 e$$^{-0.00693 	imes 180}$$ = 0.142\ \mathrm{M}$$

Question 11

For the reaction $$\mathrm{S_2O_8$$^{2-}$$}(aq) + 3\mathrm{I^-}(aq) \rightarrow 2\mathrm{SO_4$^{2-}}(aq) + \mathrm{I_3$^-}(aq)$$, if doubling $$[\mathrm{S_2O_8$$^{2-}$$}]$$ doubles the rate and doubling $$[\mathrm{I^-}]$$ also doubles the rate, what is the rate law?

Accepted Answer

$$	ext{rate} = k[\mathrm{S_2O_8$$^{2-}$$}][\mathrm{I^-}]$$

Question 12

Which of the following factors does NOT affect the rate of a chemical reaction?

Accepted Answer

The color of the reactants

Question 13

A zero-order reaction has a rate constant $$k = 0.020\ \mathrm{M\ s$$^{-1}$$}$$ and an initial concentration $$[A]_0 = 0.50\ \mathrm{M}. $$How long will it take for $$[A] to $$reach $$0.10\ \mathrm{M}$$?

Accepted Answer

$$t = \frac{[A]_0 - [A]}{k} = \frac{0.50 - 0.10}{0.020} = 20\ \mathrm{s}$$

Question 14

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

Accepted Answer

Higher temperature increases the fraction of molecules with enough energy to overcome the activation energy barrier.

Question 15

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

Accepted Answer

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

Question 16

If a reaction is first order and has a half-life of 89 s, how long does it take for 75% of the reactant to be consumed?

Accepted Answer

178 s

Question 17

Which of the following is true for a catalyst in a chemical reaction?

Accepted Answer

It lowers the activation energy without being consumed.

Question 18

For the reaction $$4\mathrm{PH_3$}(g) \rightarrow \mathrm{P_4$}(g) + 6\mathrm{H_2$}(g)$$, if $$\mathrm{H_2$} is $$being formed at $$0.078\ \mathrm{M\ s$$^{-1}$$}$$, what is the rate of disappearance of $$\mathrm{PH_3$}$$?

Accepted Answer

$$0.052\ \mathrm{M\ s$$^{-1}$$}$$

Chemical Kinetics: Rates, Laws, and Reaction Orders

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