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Reaction Kinetics: Rate Laws

Problems and Solutions

Fundamentals of Rate Laws

Determining the Rate Law

Problem :

Describe the difference between the rate constant and the rate of a reaction.

The rate of a reaction is the change in concentration with respect to time of a product. The rate equals the rate constant times the concentrations of the reactants raised to their orders. A rate constant is a proportionality constant in the rate law that is a measure of the intrinsic reactivity of the reaction. The rate constant does not depend on the concentrations of reactants but the rate does (if it is not zero order).

Problem :

What is the order of the following reaction?

There is not enough information to solve this problem. The order of a reaction must be experimentally determined. The order and stoichiometry of a reaction are causally disconnected.

Problem :

If a reaction has an order of three, write three rate laws that could describe the reaction.

rate = k [A]3
rate = k [A]2 [B]
rate = k [A] [B]2
rate = k [A] [B] [C], etc.

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