The exponents in a rate law have no relationship to the...

Name: Problem 5, Chapter 13: General Chemistry
Uploaded: 2021-06-28T02:46:39-08:00
Duration: 6 min 59 s
Channel: Preeti Kumari
Description: The exponents in a rate law have no relationship to the coefficients in the overall balanced equation for the reaction. Give an example of a balanced equation and the rate law for a reaction that clearly demonstrates this.

The exponents in a rate law have no relationship to the coefficients in the overall balanced equation for the reaction. Give an example of a balanced equation and the rate law for a reaction that clearly demonstrates this.

Key Concepts

Elementary Step

An elementary step is a single reaction event that occurs in one go and has a rate law that directly relates to its molecularity. For elementary steps, the exponents in the rate law match the number of molecules colliding, but the overall reaction is generally composed of multiple elementary steps, leading to overall rate laws that do not directly reflect the overall stoichiometry.

Rate-Determining Step

The rate-determining step is the slowest step in a reaction mechanism, controlling the overall reaction rate. Since the rate law depends on this step, its concentration dependencies set the reaction order, which might be different from what the overall balanced equation suggests based on stoichiometric coefficients.

Rate Law

A rate law expresses the relationship between the reaction rate and the concentration of reactants. It is determined empirically and reflects the step or steps that control the speed of the reaction rather than the stoichiometric coefficients of the overall balanced equation.

Reaction Mechanism

The reaction mechanism is the sequence of individual steps that make up the overall reaction. The rate law is based on the slowest (rate-determining) step in this sequence, which may not involve all reactants in their stoichiometric ratios, meaning that the observed orders in the rate law often differ from the coefficients in the balanced overall reaction.

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