Effect of Temperature Changes on Liquid-Phase Activity Coefficients

2 Effect of Temperature Changes on Liquid-Phase Activity Coefficients 

Example 9.7 Estimate the activity coefficient of ethanol in a liquid of 0.1238 mol fraction ethanol, balance water, at 70°C and 1.00 atm. 

FIGURE 9A Values of hi — h°) for ethanol (species a) and water (species b) calculated from measured heats of mixing. The two sets of curves, from the lowest to the highest, correspond to 298.15, 323.15, 331.15, 343.15, 363.15, and 383.15 K. The triangles and circles are comparisons to data from another author. (From Larkin, J. A. Thermodynamic properties of aqueous nonelectrolyte mixtures, I excess enthalpy for water + ethanol at 298.15 to 383.15 K. J. Chem. Thermodyn. 7 137-148 (1975). Reproduced hy permission of the puhhsher.) 

We find that a temperature change of 15°C changes the ethanol activity coefficient by 0.9%. The previous example showed that a pressure change of 9 atm changed the activity coefficient by 0.15%. Thus, we see that for small changes in temperature and pressure we can normally ignore the changes in liquid-phase activity coefficients. However, if 

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