The rate of a reaction is measured by the change in concentration over time. The rate of reaction is how fast the reactants are being used up or how fast a product is formed. The rate of reaction is fastest at the start of a reaction then decreases as the reactants are used up and their concentrations fall. Once all the reactants are used up the reaction ends and the rate is equal to zero.
| rate of reaction | = | change in concentration |
| | time |
A graph of change concentration of reactant (or product) can be plotted against time. The rate of reaction can be found from the
gradient of the tangent at any time t. The rate of reaction has units: moldm
-3s
-1