Abstract
Abstract : The extension of the concept of isokinetic conditions into the dimension of pressure is discussed. The use of the enthalpy and entropy of activation at constant pressure and of the energy and entropy of activation at constant volume to characterize activated processes is discussed, and it is concluded that neither set can be rigorously justified as easier to understand, but that the constantvolume parameters are probably to be preferred most of the time. The effect of pressure up to 3 kbar on the rate of the acid-catalyzed hydrolysis of methyl acetate and ethylene oxide in acetone+water mixtures was measured. The constant-volume parameters of activation for the acid-catalyzed hydrolysis of methyl acetate vary with solvent in a less complicated way than the constantpressure parameters, the minima in the constantpressure parameters not being present in the constantvolume parameters. The existence of the minima in the constant-pressure parameters is ascribed mainly to the large change of thermal expansivity when an organic liquid is added to water. The effect of solvent on the rate of hydrolysis of methyl acetate is dependent on the pressure, and reverses sign at about 2 kbar. The implications of this observation in the determination of reaction mechanisms is discussed. (Author)
Published Version
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