Energy of Activation and Water Structure

Abstract

Instances of temperature-dependent apparent energies of activation EA' observed for hydrolysis reactions, are briefly reviewed, as are recent calculations according to which the presence of a reactant in two forms which are in mobile equilibrium may lead to a temperature-dependent EA. These calculations are extended to a consideration of the temperature-dependence of the specific heat of activation, and to the possibility of more than two forms being in equilibrium. It is shown in some detail how the equilibrium between broken and intact hydrogen bonds in water may be responsible for observed effects.

The Temperature‐Dependence of E a

“…232 BERTA PERLMUTTER-HAYMAN to all theories, and is more easily visualized than that of the pre-exponential factor, that we here consider dEa/dT instead of RTd In AIdT (126). We shall then consider some results of the transition state theory, and describe two mathematical forms in which the temperature-dependence of In k and of Ea can conveniently be expressed.…”

“…104a for a compilation of data). This should be understood in the sense of "freezing" of degrees of freedom rather than any similarity to ice (46,126). It is assumed that the water molecules which solvate the ions become partly immobilized, losing some of their rotational freedom.…”

“…However, the positive values of dEa/dT in the acid-catalyzed hydrolysis of dichromate in the presence of tetramethylammonium ions (95) were explained on the basis of Eq.90, the two different forms of reactant being assumed, again, to be hydrogen-bonded and close-packed water molecules (126). However, the positive values of dEa/dT in the acid-catalyzed hydrolysis of dichromate in the presence of tetramethylammonium ions (95) were explained on the basis of Eq.90, the two different forms of reactant being assumed, again, to be hydrogen-bonded and close-packed water molecules (126).…”