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Contents

Reaction Kinetics: Rate Laws

Problems and Solutions

Determining the Rate Law

How to Cite This SparkNote

Problem :

Given the below initial rate data, determine the rate law and rate constant for the following reaction:

Using the method of initial rates, we take the ratio of rates between reactions 2 and 1 to determine the order of the reaction in permanganate.

By taking the ratios of the rates of experiments 3 and 1 we can obtain the order of the reaction in chlorite.

Finally, by taking the ratios of the rates of experiments 4 and 1 we can obtain the order of the reaction in H+.

Now that we know the order of the reaction in permanganate is 2, chlorite is 1, and H+ is 1/2, we can use the rate and concentration data in experiment 1 to calculate the rate constant.

Problem :

What is the half-life of a zero order reaction?

Starting with the integrated rate law for a zero order reaction, we rearrange the variables so we can make the substitution that [A] / [A]o = 0.5 when t = t1/2, we derive the following equation:

Problem :

Given the following rate data concerning the decomposition of sodium azide into nitrogen gas, determine its rate law including the rate constant with the appropriate units. This reaction is used to produce the gas needed to inflate airbags.

The graph of ln [HN3] versus time is linear:

That means the reaction is a first order decay process with a rate law rate = k [NaN3]. The value of k is the negative of the value of the slope, so k = 0.056 s-1.

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