Determining Order of Reaction

For a chemical reaction, the rate law expresses the relationship between the reaction rate and reactant concentration. The exponents of the reactant concentrations influence the reaction rate individually and are called reaction orders.

The reaction order is determined experimentally by employing the method of initial rates, where a chemical reaction is repeated multiple times with varying reactant concentrations to measure the initial reaction rates.

An increase in the reactant concentration, producing a linearly-proportional increase in the reaction rate, characterizes a first-order reaction. If doubling the reactant concentration quadruples the initial rate, then a second-order reaction is observed.

However, if the change of reactant concentrations does not affect the initial rate values, then a zero-order reaction is observed.

When the obtained data of initial rates present an indiscernible relationship between the change in initial reactant concentration and the corresponding rate, a ratio of rate laws is calculated.

Here, any two concentration values of the reactant and their corresponding reaction rates are used to determine the reaction order.

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