Partial molar quantities in ideal mixtures

With the help of Eq. 9.4.8 for the chemical potential of a constituent of an ideal mixture, we will now be able to find expressions for partial molar quantities. These expressions find their greatest use for ideal liquid and solid mixtures. 

For the partial molar entropy of substance i, we have Si = (from Eq. 

Since In xt is negative in a mixture, the partial molar entropy of a constituent of an ideal mixture is greater than the molar entropy of the pure substance at the same T and p. 

Hi in an ideal mixture is independent of the mixture composition and is equal to the molar enthalpy of pure i at the same T and as the mixture. In the case of an ideal gas mixture, Hi is also independent of p, because the molar enthalpy of an ideal gas depends only on T. 

Note that in an ideal mixture held at constant T and p, the partial molar quantities Hi, Vi, Ui, and Cp,i do not vary with the composition. This is basically because of tbe absence of intermolecular forces in an ideal mixture. 

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