WORKED EXAMPLE \( 12.5 \) The decomposition of hydrogen peroxide in dilute sodium hydroxide solution is described by the equation \[ 2 \mathrm{H}_{2} \mathrm{O}_{2}(a q) \longrightarrow 2 \mathrm{H}_{2} \mathrm{O}(l) \text { at } \mathrm{O}_{2}(g) \] The reaction is first order in \( \mathrm{H}_{2} \mathrm{O}_{2} \), the rate constant for consumption of \( \mathrm{H}_{2} \mathrm{O}_{2} \) at \( 20^{\circ} \mathrm{C} \) is \( 1.8 \times 10^{-5} \mathrm{~s}^{-1} \), and the initial concentration of \( \mathrm{H}_{2} \mathrm{O}_{2} \) is \( 0.30 \mathrm{M} \). (a) What is the concentration of \( \mathrm{H}_{2} \mathrm{O}_{2} \) after \( 4.00 \mathrm{~h} \) ? (b) How long will it take for the \( \mathrm{H}_{2} \mathrm{O}_{2} \) concentration to drop to \( 0.12 \mathrm{M} \) ? (c) How long will it take for \( 90 \% \) of the \( \mathrm{H}_{2} \mathrm{O}_{2} \) to decompose? 45
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Consider the first-order decomposition of $\mathrm{H}_{2} \mathrm{O}_{2}$ in Worked Example $12.5 .$ (a) What is the half-life (in hours) of the reaction at $20^{\circ} \mathrm{C} ?$ (b) What is the molarity of $\mathrm{H}_{2} \mathrm{O}_{2}$ after four half-lives if the initial concentration of $\mathrm{H}_{2} \mathrm{O}_{2}$ is 0.30 $\mathrm{M}$ ? (c) How many hours will it take for the concentration to drop to 25$\%$ of its initial value?
The decomposition of hydrogen peroxide is a firstorder reaction: $$ \mathrm{H}_{2} \mathrm{O}_{2}(a q) \longrightarrow \mathrm{H}_{2} \mathrm{O}(l)+\frac{1}{2} \mathrm{O}_{2}(g) $$ The half-life of the reaction is 17.0 minutes. a. What is the rate constant of the reaction? b. If you had a bottle of $\mathrm{H}_{2} \mathrm{O}_{2},$ how long would it take for $86.0 \%$ to decompose? c. If you started the reaction with $\left[\mathrm{H}_{2} \mathrm{O}_{2}\right]=0.100 M,$ what would be the hydrogen peroxide concentration after 15.0 minutes?
The decomposition of hydrogen peroxide is a first-order reaction: $$\mathrm{H}_{2} \mathrm{O}_{2}(a q) \longrightarrow \mathrm{H}_{2} \mathrm{O}(l)+\frac{1}{2} \mathrm{O}_{2}(g)$$ The half-life of the reaction is $17.0$ minutes. a. What is the rate constant of the reaction? b. If you had a bottle of $\mathrm{H}_{2} \mathrm{O}_{2}$, how long would it take for $86.0 \%$ to decompose? C. If you started the reaction with $\left[\mathrm{H}_{2} \mathrm{O}_{2}\right]=0.100 M$, what would be the hydrogen peroxide concentration after $15.0$ minutes?
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