An interesting result is obtained when the instantaneous rate of reaction is calculated at various points along the curve in the graph in the previous section. The rate of reaction at every point on this curve is directly proportional to the concentration of phenolphthalein at that moment in time.

Rate = k(phenolphthalein)

Because this equation is an experimental law that describes the rate of the reaction, it is called the rate law for the reaction. The proportionality constant, k, is known as the rate constant.

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