Vapour Pressure Study of Deuterium Exchange Reactions in Water-Ethanol Systems: Equilibrium Constant Determination

Abstract

A method is proposed for the determination of the equilibrium constants of liquid-phase deuterium exchange reactions from vapour pressure measurements. It is applied to water-ethanol systems to give the equilibrium constant of the reaction

2C₂H₅OH(l) + D₂(l) → 2C₂H₅OD(l) + H₂O(l)

The value obtained, 1.05+0.02 at 298 K, is significantly greater than the 'random' value and is more precise and reasonable than a recent calorimetric estimate. Vapour pressures at 298.14 K are reported for the systems H₂O+C₂H₅OH, H₂O+C₂H₅OD, D₂O + C₂H₅OH and D₂O + C₂H₅OD. Molar excess Gibbs functions are obtained from these vapour pressure measurements.