The vapor pressure of dichloromethane is measured as a function of temperature, and the results shown in the table below are obtained. Determine the heat of vaporization of dichloromethane.

Question

Temperature (K)	Vapor Pressure (torr)
200	0.8
220	4.5
240	21
260	71
280	197
300	391

Accepted Answer

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[latex]_{vap}[/latex]/R, we find the heat of vaporization as follows:

slope = -∆H[latex]_{vap}[/latex]/R
∆H[latex]_{vap}[/latex] = -slope × R
= -(-3805 K)(8.314 J/mol . K)
= 3.16 × 10[latex]^{4}[/latex] J/mol
= 3.16 kJ/mol

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

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