   Chapter 12, Problem 112CP

Chapter
Section
Textbook Problem

# Hydrogen peroxide and the iodide ion react in acidic solution as follows: H 2 O 2 ( a q ) + 3 I − ( a q ) + 2 H + ( a q ) → I 3 − ( a q ) + 2H 2 O ( l ) The kinetics of this reaction were studied by following the decay of the concentration of H2O2 and constructing plots of ln[H2O2] versus time. All the plots were linear and all solutions had [H2O2]0 = 8.0 × 10−4 mol/L. The slopes of these straight lines depended on the initial concentrations of I− and H+. The results follow: [I−]0 (mol/L) [H+]0 (mol/L) Slope (min−1) 0.1000 0.0400 − 0.120 0.3000 0.0400 − 0.360 0.4000 0.0400 − 0.480 0.0750 0.0200 − 0.0760 0.0750 0.0800 − 0.118 0.0750 0.1600 − 0.174 The rate law for this reaction has the form Rate = − Δ [ H 2 O 2 ] Δ t = ( k 1 + k 2 [ H + ] ) [ I − ] m [ H 2 O 2 ] n a. Specify the order of this reaction with respect to [H2O2] and [I−].b. Calculate the values of the rate constants, k1 and k2.c. What reason could there be for the two-term dependence of the rate on [H+]?

(a)

Interpretation Introduction

Interpretation: The order of the reaction is to be specified with respect to the reactants. The values of the rate constants are to be calculated. The reason corresponds to the fact that two-term dependence of the rate on the concentration of H+ ion is to be stated.

Concept introduction: The order of a reaction is the number or the index raise to the concentration term with respect to each component

The rate law or rate equation is a mathematical representation that relates the rate of the reaction with the concentration or pressure.

Rate constant is a proportionality coefficient that relates the rate of chemical reaction at a specific temperature to the concentration of the reactant or the product.

To determine: The order of the reaction with respect to [H2O2] and [I].

Explanation

Explanation

The order of the reaction with respect to [H2O2] and [I] is zero and first order respectively.

Given

The given reaction is stated as,

H2O2(aq)+3I(aq)+2H+(aq)I3(aq)+2H2O(l)

The plot of ln[H2O2] Vs time is linear.

The concentration of [H2O2]0=8.00×104M

The rate law for the reaction,

Rate=Δ[H2O2]Δt=(k1+k2[H+])[I]m[H2O2]n

The concentration of [H2O2] is very small which is given above. The concentration of [H+] and [I] is significant. Therefore, the reduced form of rate law is represented as,

d[H2O2]dt=kobserved[H2O2]n

Where,

• kobserved=(k1+k2[H+])[I]m

The concentration of H2O2 is very small indicates that the reaction is independent of the reactant H2O2

Therefore reaction is zero order with respect to the reactant H2O2

(b)

Interpretation Introduction

Interpretation: The order of the reaction is to be specified with respect to the reactants. The values of the rate constants are to be calculated. The reason corresponds to the fact that two-term dependence of the rate on the concentration of H+ ion is to be stated.

Concept introduction: The order of a reaction is the number or the index raise to the concentration term with respect to each component

The rate law or rate equation is a mathematical representation that relates the rate of the reaction with the concentration or pressure.

Rate constant is a proportionality coefficient that relates the rate of chemical reaction at a specific temperature to the concentration of the reactant or the product.

To determine: The value of the rate constant k1 and k2 for the given reaction.

(c)

Interpretation Introduction

Interpretation: The order of the reaction is to be specified with respect to the reactants. The values of the rate constants are to be calculated. The reason corresponds to the fact that two-term dependence of the rate on the concentration of H+ ion is to be stated.

Concept introduction: The order of a reaction is the number or the index raise to the concentration term with respect to each component

The rate law or rate equation is a mathematical representation that relates the rate of the reaction with the concentration or pressure.

Rate constant is a proportionality coefficient that relates the rate of chemical reaction at a specific temperature to the concentration of the reactant or the product.

To determine: The reason for the two-term dependence of the rate on [H+]

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