Chapter 15

What are the four basic steps involved in heterogeneous catalysis?

What are enzymes? What is the active site of an enzyme? What is a substrate?

What is the general two-step mechanism by which most enzymes work?

\(\begin{aligned} \text { Consider the reaction. } \\ & 2 \operatorname{HBr}(g) \longrightarrow \mathrm{H}_{2}(g)+\mathrm{Br}_{2}(g) \end{aligned}\) \begin{equation} \begin{array}{l}{\text { a. Express the rate of the reaction in terms of the change in concen- }} \\ {\text { tration of each of the reactants and products. }}\end{array} \end{equation} \begin{array}{l}{\text { b. In the first } 25.0 \text { s of this reaction, the concentration of HBr drops }} \\ {\text { from } 0.600 \mathrm{M} \text { to } 0.512 \mathrm{M} \text { . Calculate the average rate of the reac- }} \\\ {\text { tion during this time interval. }} \\ {\text { c. If the volume of the reaction vessel in part b is } 1.50 \mathrm{L}, \text { what }} \\ {\text { amount of } \mathrm{Br}_{2}(\text { in moles) forms during the first } 15.0 \mathrm{s} \text { of the }} \\ {\text { reaction? }}\end{array}

\(\begin{aligned} \text { Consider the reaction. } \\ & 2 \mathrm{N}_{2} \mathrm{O}(g) \longrightarrow 2 \mathrm{N}_{2}(g)+\mathrm{O}_{2}(g) \end{aligned}\) \begin{equation} \begin{array}{l}{\text { a. Express the rate of the reaction in terms of the change in }} \\ {\text { concentration of each of the reactants and products. }} \\ {\text { b. In the first } 15.0 \text { s of the reaction, 0.015 mol of } \mathrm{O}_{2} \text { is produced in a }} \\ {\text { reaction vessel with a volume of } 0.500 \text { L. What is the average rate }} \\ {\text { of the reaction during this time interval? }}\end{array} \end{equation} \begin{equation} \begin{array}{l}{\text { c. Predict the rate of change in the concentration of } \mathrm{N}_{2} \mathrm{O} \text { during this }} \\ {\text { time interval. In other words, what is } \Delta\left[\mathrm{N}_{2} \mathrm{O}\right] / \Delta t?}\end{array} \end{equation}

For the reaction \(2 \mathrm{A}(g)+\mathrm{B}(g) \longrightarrow 3 \mathrm{C}(g),\) \begin{equation} \begin{array}{l}{\text { a. determine the expression for the rate of the reaction in terms of }} \\ {\text { the change in concentration of each of the reactants and products. }} \\ {\text { b. when A is decreasing at a rate of } 0.100 \mathrm{M} / \mathrm{s} \text { , how fast is } \mathrm{B} \text { decreas- }} \\ {\text { ing? How fast is Cincreasing? }}\end{array} \end{equation}

For the reaction \(\mathrm{A}(g)+\frac{1}{2} \mathrm{B}(g) \longrightarrow 2 \mathrm{C}(g),\) \begin{equation} \begin{array}{l}{\text { a. determine the expression for the rate of the reaction in terms of }} \\ {\text { the change in concentration of cach of the reactants and products. }} \\ {\text { b. when } C \text { is increasing at a rate of } 0.0025 \mathrm{M} / \mathrm{s} \text { , how fast is } \mathrm{B}} \\ {\text { decreasing? How fast is A decreasing? }}\end{array} \end{equation}

What are the units of \(k\) for each type of reaction? \begin{equation} \begin{array}{l}{\text { a. first-order reaction }} \\ {\text { b. second- order reaction }} \\ {\text { c. } \text { zero-order reaction }}\end{array} \end{equation}

This reaction is first order in \(\mathrm{N}_{2} \mathrm{O}_{5}:\) $$\mathrm{N}_{2} \mathrm{O}_{5}(g) \longrightarrow \mathrm{NO}_{3}(g)+\mathrm{NO}_{2}(g)$$ The rate constant for the reaction at a certain temperature is 0.053\(/ \mathrm{s}.\) \begin{equation} \begin{array}{l}{\text { a. Calculate the rate of the reaction when }\left[\mathrm{N}_{2} \mathrm{O}_{5}\right]=0.055 \mathrm{M} \text { . }} \\\ {\text { b. What is the rate of the reaction at the concentration indicated in part }} \\ {\text { a if the reaction is second order? Zero order? (Assume the same } n u-} \\ {\text { merical value for the rate constant with the appropriate units.) }}\end{array} \end{equation}

A reaction in which \(\mathrm{A}, \mathrm{B},\) and C react to form products is first order in \(\mathrm{A},\) second order in \(\mathrm{B},\) and \(\mathrm{zero}\) order in \(\mathrm{C}\) . \begin{equation} \begin{array}{l}{\text { a. Write a rate law for the reaction. }} \\ {\text { b. What is the overall order of the reaction? }} \\ {\text { c. By what factor does the reaction rate change if }[A] \text { is doubled (and the }} \\\ {\text { other reactant concentrations are held constant)? }}\end{array} \end{equation} \begin{equation} \begin{array}{l}{\text { d. By what factor does the reaction rate change if }[\mathrm{B}] \text { is doubled (and the }} \\ {\text { other reactant concentrations are held constant)? }} \\ {\text { e. By what factor does the reaction rate change if }[\mathrm{C}] \text { is doubled (and the }} \\\ {\text { other reactant concentrations are held constant)? }}\\\\{\text { f. By what factor does the reaction rate change if the concentrations of }} \\\ {\text { all three reactants are doubled? }}\end{array} \end{equation}