Determination of Henry's law constants for aqueous solutions of tetradeuteriomethane between 285 and 325 K and calculation of the H/D isotope effect

Original data for the solubility of deuteriomethane in water were obtained experimentally as a function of temperature. By comparison with literature data for the solubility of methane in water, the solute deuterium isotope e ffect on the Henry's law constants of methane in water could be determined quantitatively. A high-precision experimental method was used to determine Henry's law coefficients from solubility measurements of deuterated methane in pure liquid water in the temperature range 285 to 325 K and at pressure s close to atmospheric. The temperature dependence of the Henry's law coeff icients is accounted for by appropriate semiempirical correlations. The imp recision of the experimental data, as determined by the average absolute de viations of Henry's law coefficients from the smoothing equations, is appro ximately +/-0.05%. From the temperature variation of the solubility, partia l molar quantities characteristic of the solution such as the standard chan ges in Gibbs energy, enthalpy, entropy and heat capacity have been determin ed. We have observed that CD4 is less soluble in water (inverse isotope eff ect), its Henry's law constant being, on average, 1.6% higher in the temper ature range studied.