Chapter 15: Problem 2
Why are reaction rates important (both practically and theoretically)?
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Chapter 15: Problem 2
Why are reaction rates important (both practically and theoretically)?
These are the key concepts you need to understand to accurately answer the question.
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The reaction \(2 \mathrm{H}_{2} \mathrm{O}_{2}(a q) \longrightarrow 2 \mathrm{H}_{2} \mathrm{O}(l)+\mathrm{O}_{2}(g)\) is first order in \(\mathrm{H}_{2} \mathrm{O}_{2}\) and under certain conditions has a rate constant of 0.00752 \(\mathrm{s}^{-1}\) at \(20.0^{\circ} \mathrm{C} .\) A reaction vessel initially contains 150.0 \(\mathrm{mL}\) of 30.0\(\%\) \(\mathrm{H}_{2} \mathrm{O}_{2}\) by mass solution (the density of the solution is 1.11 \(\mathrm{g} / \mathrm{mL} )\) . The gaseous oxygen is collected over water at \(20.0^{\circ} \mathrm{C}\) as it forms. What volume of \(\mathrm{O}_{2}\) forms in 85.0 seconds at a barometric pressure of 742.5 \(\mathrm{mmHg}\) ? (The vapor pressure of water at this temperature is 17.5 \(\mathrm{mm} \mathrm{g} . )\)
The activation barrier for the hydrolysis of sucrose into glucose and fruc- tose is 108 \(\mathrm{k} / \mathrm{mol}\) . If an enzyme increases the rate of the hydrolysis reac- tion by a factor of 1 million, how much lower must the activation barrier be when sucrose is in the active site of the enzyme? (Assume that the frequency factors for the catalyzed and uncatalyzed reactions are identi- cal and a temperature of \(25^{\circ} \mathrm{C.})\)
A chemical reaction is endothermic and has an activation energy that is twice the value of the enthalpy change of the reaction. Draw a dia- gram depicting the energy of the reaction as it progresses. Label the position of the reactants and products and indicate the activation ener- gy and enthalpy of reaction.
The desorption of a single molecular layer of \(n\) -butane from a single crystal of aluminum oxide is found to be first order with a rate constant of 0.128\(/ \mathrm{s}\) at 150 \(\mathrm{K}\) . \begin{equation} \begin{array}{l}{\text { a. What is the haff-life of the desorption reaction? }} \\ {\text { b. If the surface is initially completely covered with } n \text { -butane at }} \\ {150 \mathrm{K}, \text { how long will it take for } 25 \% \text { of the molecules to desorb? For }} \\ {50 \% \text { to desorb? }}\\\\{\text { c. If the surface is initially completely covered, what fraction will remain }} \\ {\text { covered after } 10 \text { s? After } 20 \mathrm{s?}}\end{array} \end{equation}
This reaction has an activation energy of zero in the gas phase. $$\mathrm{CH}_{3}+\mathrm{CH}_{3} \longrightarrow \mathrm{C}_{2} \mathrm{H}_{6}$$ \begin{equation} \begin{array}{l}{\text { a. Would you expect the rate of this reaction to change very much }} \\ {\text { with temperature? }} \\ {\text { b. Why might the activation energy be zero? }} \\ {\text { c. What other types of reactions would you expect to have little or no }} \\ {\text { activation energy? }}\end{array} \end{equation}
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