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 effect 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 pressures close to atmospheric. The temperature dependence of the Henry's law coefficients is accounted for by appropriate semiempirical correlations. The imprecision of the experimental data, as determined by the average absolute deviations of Henry's law coefficients from the smoothing equations, is approximately ± 0.05%. From the temperature variation of the solubility, partial molar quantities characteristic of the solution such as the standard changes in Gibbs energy, enthalpy, entropy and heat capacity have been determined. We have observed that CD4 is less soluble in water (inverse isotope effect), its Henry's law constant being, on average, 1.6% higher in the temperature range studied.