The partial excess thermodynamic properties of hydrogen in palladium

New measurements of the hydrogen chemical potential and the partial enthalpy of hydrogen in Pd-H alloys are reported. These results are combined with information available in the literature to obtain a consistent set of values for the partial excess enthalpy and entropy of hydrogen as a function of composition. The partial excess entropy of hydrogen varies from negative values at low hydrogen concentrations to positive values at high hydrogen concentrations and it is demonstrated that the principal contribution to this excess entropy is configurational. Problems associated with trying to interpret these properties in terms of pairwise interaction models are discussed.