A new relationship based on the Hammett equation is derived for the esterification reaction of substituted carboxylic acid in the presence of hydrated sulphate salts and is called a catalyzing linear free energy equation. The equation can be expressed as log(KR(M)/K0Mn))=\s\*\T\^M + Ym where KR(M) is the rate constant of the esterification reaction of substituted acetic acid catalyzed by hydrated sulphate salts of M matal, K0(Mn) is the rate constant of that of acetic acid catalyzed by MnSO4.H2O, Ym is active index of catalyst. For reactions catalyzed by certain catalysts the rate constant of substituted acetic acid can be estimated from the equation.

Key words: CARBOXYLIC ACID, ETHANOL, CATALYST, ESTERIFICATION, ACTIVITY, SULFATE, HYDRATE, LINEAR FREE ENERGY RELATIONSHIP