The Phase Rule—a Method of Classifying All Systems in Equilibrium

Example 10-8. The vapor pressure of water at 0°C is 0.0060 atm. What is the heat of vaporization of water  

We may replace [H20(l)] by a constant, and incorporate it into the equilibrium constant  

Thus we have obtained 45.3 kJ mole as the heat of vaporization of water over the temperature range 0°C to 100°C, with the assumption that it is constant over this range. 

By use of values of the vapor pressure over smaller ranges of temperature the same procedure leads to 45.3 kJ mole at 0°C, 42.8 kJ mole at 50°C, and 40.7 kJ mole at 100°C. These values are verified by calorimetric measurements. 

The Phase Rule—a Method of Classifying All Systems in Equilibrium 

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