Question

The normal boiling point of Substance A is 129.4 °C. Given that the vapor pressure of Substance A is 481.9 torr at 8.5 °C, calculate the molar enthalpy of vaporization to the nearest kJ/mol

Answer 1

Problem #8: A 5.00 L flask contains 3.00 g of mercury. The system is at room temperature of 25.0 °C. By how many degrees should we increase the temperature of the flask to triple the mercury vapor pressure. The enthalpy of vaporization for mercury is 59.11 kJ/mol?

Solution:

1) Let us use the Clausius-Clapeyron Equation:

with the following values:

P1 = 1 T1 = 298 K

P2 = 3 T2 = x

3) Set up equation with values:

ln (3/1) = (59110 / 8.31447) (1/298 minus 1/x)

1.0968 = 7109.2926 (1/298 minus 1/x)

1.0968 = 23.8567 minus 7109.2926/x)

x = 312.4 K = 39.4 °C