PPT Slide

9

The relation between vapor pressure and temperature.

• The non-linear relationship between vapor pressure and temperature can be expressed mathematically in linear form:

ln P is the natural logarithm of the vapor pressure.

_H vap = heat of vaporization.

R = universal gas constant (8.31 J/mol.K).

T is the absolute temperature, and C is a constant.

Clausius-Clapeyron equation:

• A two-point version of the equation allows determination of _H vap :

Using the Clausius-Clapeyron Equation

Problem: The vapor pressure of ethanol is 115 torr at 34.9ƒC. If _H vap of C 2H 5OH is 40.5 kJ/mol, calculate the temperature (in ƒC) when the vapor pressure is 760 torr.

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