第5章-相平衡.pptPPT.ppt

Simple mixtures The partial molar volumes of water and ethanol at 25(C. Note the different scales (water on the left, ethanol on the right). Simple mixtures Simple mixtures The partial molar volume of a substance is the slope of the variation of the total volume of the sample plotted against the composition. In general, partial molar quantities vary with the composition, as shown by the different slopes at the compositions a and b. Note that the partial molar volume at b is negative: the overall volume of the sample decreases as a is added. Simple mixtures Simple mixtures The chemical potential of a substance is the slope of the total Gibbs energy of a mixture with respect to the amount of substance of interest. In general, the chemical potential varies with composition, as shown for the two values at a and b. In this case, both chemical potentials are positive. Simple mixtures Simple mixtures The partial molar volumes of the components of an aqueous solution of potassium sulfate. Simple mixtures The Gibbs energy of mixing of two perfect gases and (as discussed later) of two liquids that form an ideal solution. The Gibbs energy of mixing is negative for all compositions and temperatures, so perfect gases mix spontaneously in all proportions. Simple mixtures Simple mixtures The initial and final states considered in the calculation of the Gibbs energy of mixing of gases at different initial pressures. Simple mixtures Simple mixtures The entropy of mixing of two perfect gases and (as discussed later) of two liquids that form an ideal solution. The entropy increases for all compositions and temperatures, so perfect gases mix spontaneously in all proportions. Because there is no transfer of heat to the surroundings when perfect gases mix, the entropy of the surroundings is unchanged. Hence, the graph also shows the total entropy of the system plus the surroundings when perfect gases mix. Simple mixtures Simple mixtures At equilibrium, the chemical potential of th