Question

Benzene has a heat of vaporization of 30.72 kJ/mol and a normal boiling point of 80.1 °C. At what temperature does benzene boil when the external pressure is 445 torr?

Answer 1

Heat of vaporization of benzene is 30.72 kJ/mol.

Norma boiling point:

The normal boiling point of a liquid is the temperature at which its vapor pressure equals 1 atm.

Normal boiling point of benzene is .

Calculate the temperature at which benzene boils at vapor pressure of 445 torr.

Consider the Clausius-Clapeyron equation as follows:

Here, is the vapor pressure of benzene at temperature , and is the vapor pressure of benzene at temperature , R is the gas constant, and is the heat of vaporization.

From the definition of normal boiling point, vapor pressure of benzene at normal boiling point is 1 atm.

Hence, vapor pressure of benzene at is 1 atm.

Hence,

So, substitute the values in the Clausius-Clapeyron equation as follows:

Convert the temperature in kelvin to as follows:

Therefore, the temperature at which benzene boils at 445 torr vapor pressure is .