Vapor-liquid equilibria of formic acid-methanol and formic acid-ethanol systems which are accompanied with esterification reaction were measured at atmospheric pressure.
The relation of vapor-liquid equilibrium ratio（y_i/x_i） and temperature were obtained from the measured data. The activity coefficients of formic acid were calculated from the measured data and the dimerization equilibrium constant, taking into account association of vapor phase. For the other components, the activity coefficients were calculated by regarding vapor phase as an ideal gas, and the gradients of the activity coefficients vs. 1/T were about zero. Accordingly, the gradients of vapor liquid equilibrium ratio vs. temperature were compared with the values calculated from the molal latent heat of vaporization, and the values were found to be in good agreement.
As a result, isobaric vapor-liquid equilibrium accompanied with reaction could be correlated with molal latent heat of vaporization.