Question 11.4: The vapor pressure of dichloromethane is measured as a funct...

To find the heat of vaporization, use an Excel spreadsheet or a graphing calculator to make a plot of the natural log of vapor pressure (ln P) as a function of the inverse of the temperature in kelvins (1/T). Then fit the points to a line and determine the slope of the line. The slope of the bestfitting line is -3805 K. Since the slope equals -∆H_{vap}/R, we find the heat of vaporization as follows:

slope = -∆H_{vap}/R
∆H_{vap} = -slope × R
= -(-3805 K)(8.314 J/mol . K)
= 3.16 × 10^{4} J/mol
= 3.16 kJ/mol