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Ch.14 - Chemical Kinetics
All textbooksMcMurry 8th EditionCh.14 - Chemical KineticsProblem 126b
Chapter 14, Problem 126b

Consider the following concentration–time data for the reaction of iodide ion and hypochlorite ion (OCl-). The products are chloride ion and hypoiodite ion (OI-).
(b) Determine the rate law, and calculate the value of the rate constant.

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Identify the general form of the rate law for the reaction: Rate = k[I^-]^m[OCl^-]^n, where k is the rate constant, and m and n are the reaction orders with respect to iodide and hypochlorite ions, respectively.
Use the concentration-time data to determine the reaction orders m and n. This can be done by comparing the initial rates of reaction when the concentration of one reactant is changed while the other is held constant.
Once the reaction orders m and n are determined, substitute them back into the rate law equation.
Use the concentration-time data to calculate the rate constant k. Choose one set of concentration and rate data, substitute the values into the rate law equation, and solve for k.
Verify the calculated rate constant k by substituting it back into the rate law equation with other sets of concentration and rate data to ensure consistency.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Rate Law

The rate law expresses the relationship between the rate of a chemical reaction and the concentration of its reactants. It is typically formulated as rate = k[A]^m[B]^n, where k is the rate constant, [A] and [B] are the concentrations of the reactants, and m and n are the reaction orders with respect to each reactant. Understanding the rate law is essential for determining how changes in concentration affect the reaction rate.
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Order of Reaction

The order of a reaction refers to the exponent to which the concentration of a reactant is raised in the rate law. It indicates how the rate of reaction is affected by the concentration of that reactant. The overall order is the sum of the individual orders, and it helps in predicting the behavior of the reaction under varying conditions, which is crucial for calculating the rate constant.
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Rate Constant (k)

The rate constant (k) is a proportionality factor in the rate law that is specific to a particular reaction at a given temperature. It reflects the speed of the reaction and is influenced by factors such as temperature and the presence of catalysts. Calculating the rate constant is vital for understanding the kinetics of the reaction and allows for comparisons between different reactions.
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Related Practice
Textbook Question
Concentration–time data for the conversion of A and B to D are listed in the following table. (c) What is the rate law?

Textbook Question

Consider the following concentration–time data for the reaction of iodide ion and hypochlorite ion (OCl-). The products are chloride ion and hypoiodite ion (OI-).

(a) Write a balanced equation for the reaction.

Textbook Question

Consider the following concentration–time data for the reaction of iodide ion and hypochlorite ion (OCl-). The products are chloride ion and hypoiodite ion (OI-).

(d) Propose a mechanism that is consistent with the rate law, and express the rate constant in terms of the rate constants for the elementary steps in your mechanism. (Hint: Transfer of an H+ ion between H2O and OCl- is a rapid reversible reaction.)

Textbook Question

Consider the reversible, first-order interconversion of two molecules A and B: where kf = 3.0⨉10-3 s-1 is the rate constant for the forward reaction and kr = 1.0⨉10-3 s-1 is the rate constant for the reverse reaction. We'll see in Chapter 15 that a reaction does not go to completion but instead reaches a state of equilibrium with comparable concentrations of reactants and products if the rate constants kf and kr have comparable values.

(a) What are the rate laws for the forward and reverse reactions?

Textbook Question

Consider the reversible, first-order interconversion of two molecules A and B: where kf = 3.0⨉10-3 s-1 is the rate constant for the forward reaction and kr = 1.0⨉10-3 s-1 is the rate constant for the reverse reaction. We'll see in Chapter 15 that a reaction does not go to completion but instead reaches a state of equilibrium with comparable concentrations of reactants and products if the rate constants kf and kr have comparable values.

(b) Draw a qualitative graph that shows how the rates of the forward and reverse reactions vary with time.