Method of Initial Rates
The order of a reaction for each reactant can be estimated from the variation in initial rate with the concentration of that reactant, using the natural logarithm of the typical rate equation
For example the initial rate can be measured in a series of experiments at different initial concentrations of reactant A with all other concentrations, ... kept constant, so that
The slope of a graph of as a function of then corresponds to the order x with respect to reactant A.
However this method is not always reliable because
- measurement of the initial rate requires accurate determination of small changes in concentration in short times (compared to the reaction half-life) and is sensitive to errors, and
- the rate equation will not be completely determined if the rate also depends on substances not present at the beginning of the reaction, such as intermediates or products.
The tentative rate equation determined by this method is therefore normally verified by comparing the concentrations measured over a longer time (several half-lives) with the integrated form of the rate equation.
Read more about this topic: Order Of Reaction
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