The rate law gives us an equation that relates the reaction rate to the concentration of a species in the reaction. Since measuring reaction rates can be difficult, it it often more useful to have a relationship that directly relates the concentration of a species to the time since the reaction began

These relationships can be found by integrating the rate law. If we assume that the concentration of reactant A is [A]₀ at t=0 and [A] at time T in a reaction of type A-> products, we can seperate the variables in the rate equation and integrate. The details of the integration differ depending on the order of the species in the reaction. The table below gives the rate expression and the integrated rate expression for 0th, 1st and 2nd order reactions: click on the order to see the details.

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