The reaction $2 \mathrm{ClO}_{2}(a q)+2 \mathrm{OH}^{-}(a q) \longrightarrow \mathrm{ClO}_{3}^{-}(a q)+\( \)\mathrm{ClO}_{2}^{-}(a q)+\mathrm{H}_{2} \mathrm{O}(l)$ was studied with the following results: $$ \begin{array}{lccc} \hline \text { Experiment } & {\left[\mathrm{CIO}_{2}\right](M)} & {\left[\mathrm{OH}^{-}\right](M)} & \text { Initial Rate }(M / s) \\ \hline 1 & 0.060 & 0.030 & 0.0248 \\ 2 & 0.020 & 0.030 & 0.00276 \\ 3 & 0.020 & 0.090 & 0.00828 \\ \hline \end{array} $$ (a) Determine the rate law for the reaction. (b) Calculate the rate constant with proper units. (c) Calculate the rate when \(\left[\mathrm{ClO}_{2}\right]=0.100 \mathrm{M}\) and \(\left[\mathrm{OH}^{-}\right]=0.050 \mathrm{M}\)

Short Answer

Expert verified
(a) The rate law for the reaction is Rate = k[ClO2]^2[OH-]^1. (b) The rate constant (k) is 9.2 M^(-2)s^(-1). (c) The rate of the reaction when [ClO2] = 0.100 M and [OH-] = 0.050 M is 0.046 M/s.

Step by step solution

01

Determine the order of the reaction with respect to each reactant

From the given table, we can compare the rates of the different experiments to determine the order of the reaction with respect to each reactant. Consider experiments 1 and 2. The [ClO2] in experiment 1 is 3 times that of experiment 2, while [OH-] remains the same. Comparing the rates of these two experiments, we get: \(\frac{0.0248}{0.00276} = 9\) Since the [ClO2] increased by a factor of 3, and the rate increased by a factor of 9, we can deduce that the order of the reaction with respect to ClO2 is 2 (first order: rate increase would be 3; second order: rate increase would be \(3^2 = 9\); etc.) Now, let's consider experiments 2 and 3. The [OH-] in experiment 3 is 3 times that of experiment 2 while the [ClO2] remains the same. Comparing the rates of these two experiments, we get: \(\frac{0.00828}{0.00276} = 3\) Since the [OH-] increased by a factor of 3, and the rate increased by a factor of 3 as well, we can deduce that the order of the reaction with respect to OH- is 1 (first-order reaction since rate increase is same as concentration increase). Thus, the rate law for the reaction can be written as: Rate = k[ClO2]^2[OH-]^1
02

Calculate the rate constant

Now that we have determined the rate law, we can calculate the rate constant 'k' using the concentration and rate data from any of the experiments. We will use the data from experiment 1. Rate = k[ClO2]^2[OH-]^1 0.0248 = k(0.060)^2(0.030) Solving for k: k = \(\frac{0.0248}{(0.060)^2(0.030)}\) = 9.2 M^(-2)s^(-1) The rate constant (k) is 9.2 M^(-2)s^(-1).
03

Calculate the rate for given concentrations

Now that we have the rate law and the rate constant, we can calculate the rate of the reaction when [ClO2] = 0.100 M and [OH-] = 0.050 M. Rate = k[ClO2]^2[OH-]^1 Rate = (9.2 M^(-2)s^(-1))(0.100 M)^2(0.050 M) Rate = 0.046 M/s The rate of the reaction when [ClO2] = 0.100 M and [OH-] = 0.050 M is 0.046 M/s.

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Most popular questions from this chapter

(a) Develop an equation for the half-life of a zero-order reaction. (b) Does the half-life of a zero-order reaction increase, decrease, or remain the same as the reaction proceeds?

Consider the hypothetical reaction $2 \mathrm{~A}+\mathrm{B} \longrightarrow 2 \mathrm{C}+\mathrm{D}$. The following two-step mechanism is proposed for the reaction: $$ \begin{array}{l} \text { Step } 1: \mathrm{A}+\mathrm{B} \longrightarrow \mathrm{C}+\mathrm{X} \\\ \text { Step } 2: \mathrm{A}+\mathrm{X} \longrightarrow \mathrm{C}+\mathrm{D} \end{array} $$ \(\mathrm{X}\) is an unstable intermediate. (a) What is the predicted rate law expression if Step 1 is rate determining? (b) What is the predicted rate law expression if Step 2 is rate determining? (c) Your result for part (b) might be considered surprising for which of the following reasons: (i) The concentration of a product is in the rate law. (ii) There is a negative reaction order in the rate law. (iii) Both reasons (i) and (ii). (iv) Neither reasons (i) nor (ii).

(a) Can an intermediate appear as a reactant in the first step of a reaction mechanism? (b) On a reaction energy profile diagram, is an intermediate represented as a peak or a valley? (c) If a molecule like \(\mathrm{Cl}_{2}\) falls apart in an elementary reaction, what is the molecularity of the reaction?

Consider the reaction \(2 \mathrm{~A} \longrightarrow \mathrm{B}\). Is each of the following statements true or false? (a) The rate law for the reaction must be, Rate \(=k[\mathrm{~A}]^{2} .(\mathbf{b})\) If the reaction is an elementary reaction, the rate law is second order. \((\mathbf{c})\) If the reaction is an elementary reaction, the rate law of the reverse reaction is first order. (d) The activation energy for the reverse reaction must be smaller than that for the forward reaction.

You have studied the gas-phase oxidation of \(\mathrm{HBr}\) by \(\mathrm{O}_{2}\) : $$ 4 \mathrm{HBr}(g)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{H}_{2} \mathrm{O}(g)+2 \mathrm{Br}_{2}(g) $$ You find the reaction to be first order with respect to \(\mathrm{HBr}\) and first order with respect to \(\mathrm{O}_{2}\). You propose the following mechanism: $$ \begin{aligned} \operatorname{HBr}(g)+\mathrm{O}_{2}(g) & \longrightarrow \mathrm{HOOBr}(g) \\\ \mathrm{HOOBr}(g)+\mathrm{HBr}(g) & \longrightarrow 2 \mathrm{HOBr}(g) \\ \mathrm{HOBr}(g)+\mathrm{HBr}(g) & \longrightarrow \mathrm{H}_{2} \mathrm{O}(g)+\mathrm{Br}_{2}(g) \end{aligned} $$ (a) Confirm that the elementary reactions add to give the overall reaction. (b) Based on the experimentally determined rate law, which step is rate determining? (c) What are the intermediates in this mechanism? (d) If you are unable to detect HOBr or HOOBr among the products, does this disprove your mechanism?

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