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Chapter 13: Problem 145

True or false? The orders in a rate law are equal to the balancing coefficients in the slowest elementary step in a mechanism.

Short Answer

Expert verified
False. The orders in a rate law are not always equal to the balancing coefficients in the slowest elementary step in a mechanism. While they can be equal in some cases (e.g., for bimolecular or termolecular steps), it is important to remember that reaction orders are determined experimentally and cannot be directly inferred from stoichiometric coefficients in the balanced chemical equation.

Step by step solution

01

Understanding the Rate Law and Order of Reaction

The rate law is an expression that describes the relationship between the concentration of reactants and the speed at which a chemical reaction proceeds. The order of a reaction is the sum of the powers to which the concentrations of the reactants are raised in the rate law. The order of a reaction is determined experimentally and is not directly related to the stoichiometric coefficients in the balanced chemical equation.
02

Elementary Steps in Reaction Mechanisms

A reaction mechanism is a series of individual steps, known as elementary steps, that occur in a particular order during a chemical reaction. Each elementary step has its own rate law and molecularity. The molecularity of a reaction is the number of species involved in an elementary step and can be unimolecular, bimolecular, or termolecular.
03

Relationship Between Order and Elementary Steps

While the overall order of a reaction is found by summing the orders of the reactants in the rate-determining step (slowest step), it is important to note that these orders are not necessarily equal to the stoichiometric coefficients in the balanced chemical equation. The orders of reactants in a rate law can only be equal to the coefficients of those reactants involved in the slowest elementary step if that step is bimolecular or termolecular.
04

Verifying the Statement

The given statement is partially correct, as the orders in a rate law can be equal to the balancing coefficients in the slowest elementary step in a mechanism, but it is not always true for all cases. It is important to remember that the orders of a reaction are determined experimentally and cannot be directly inferred from the stoichiometric coefficients in the balanced chemical equation. Therefore, the statement is considered:
05

False

The orders in a rate law are NOT always equal to the balancing coefficients in the slowest elementary step in a mechanism.

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Most popular questions from this chapter

Reactions go faster when heated. Astudent claims this is because as temperature increases, the activation energy \(E_{\mathrm{a}}\) for a reaction decreases. Is this student correct or incorrect? If incorrect, then explain what happens to \(E_{\mathrm{a}}\) upon heating a reaction.

Which of the following will slow down a chemical reaction? (a) Increase concentration of reactants. (b) Add catalyst. (c) Decrease temperature. (d) All of the above.

The reaction \(\mathrm{N}_{2}+3 \mathrm{H}_{2} \rightarrow 2 \mathrm{NH}_{3}\) is exothermic. Draw a reaction-energy profile for the reaction. Label the gap that represents \(\Delta E_{\mathrm{rxn}} .\)

The experimental rate law for the reaction \(\mathrm{A}+\mathrm{A} \rightarrow \mathrm{A}_{2}\) is Rate \(=k[\mathrm{~A}][\mathrm{BC}]\) Two mechanisms have been proposed for the reaction: Step 1: \(\mathrm{A}+\mathrm{B} \rightarrow \mathrm{AB}\) (slow) Step \(2: \mathrm{AB}+\mathrm{A} \rightarrow \mathrm{A}_{2}+\mathrm{B}\) (fast) and Step \(1: \mathrm{A}+\mathrm{BC} \rightarrow \mathrm{AB}+\mathrm{C}\) (slow) Step \(2: \mathrm{A}+\mathrm{AB} \rightarrow \mathrm{B}+\mathrm{A}_{2}\) (fast) Step \(3: \mathrm{B}+\mathrm{C} \rightarrow \mathrm{BC}\) (fast) (a) Show that each mechanism results in the correct overall reaction. (b) Which mechanism is consistent with the rate law? (c) Why does \(\mathrm{BC}\) appear in the rate law but not in the overall reaction?

What is a catalyst and why is so little catalyst needed to get the desired effect?
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