Orders of Reaction and Rate Equations

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This is called the rate equation for the reaction.

The concentrations of A and B have to be raised to some power to show how they affect the rate of the reaction. These powers are called the orders of reaction with respect to A and B. The orders of reaction you are likely to meet will be 0, 1 or 2, but other values are possible including fractional ones like 1.53, for example.

If the order of reaction with respect to A is 0 (zero), this means that the concentration of A doesn't affect the rate of reaction. Mathematically, any number raised to the power of zero (x⁰) is equal to 1. That means that that particular term disappears from the rate equation.

The overall order of the reaction is found by adding up the individual orders. For example, if the reaction is first order with respect to both A and B (a = 1 and b = 1), the overall order is 2. We call this an overall second order reaction.

Contributors and Attributions

Jim Clark (Chemguide.co.uk)