Table of contents

13. Liquids, Solids & Intermolecular Forces

Clausius-Clapeyron Equation

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Multiple Choice

The vapor pressure of dichloromethane, CH2Cl2, at 0°C is 134 mmHg. The normal boiling point of dichloromethane is 40°C. Calculate its molar heat of vaporization using the Clausius-Clapeyron equation.

45.3 kJ/mol

28.7 kJ/mol

15.2 kJ/mol

60.1 kJ/mol

Verified step by step guidance

Understand the Clausius-Clapeyron equation, which relates the vapor pressure and temperature to the molar heat of vaporization. The equation is:

P^{1} = P^{2} - \frac{ΔHvap}{R \times (\frac{1}{T1}}

, where

P

is the vapor pressure,

T

is the temperature in Kelvin,

ΔHvap

is the molar heat of vaporization, and

R

is the universal gas constant.

Convert the temperatures from Celsius to Kelvin. The temperature at 0°C is 273 K, and the normal boiling point at 40°C is 313 K.

Use the given vapor pressure at 0°C, which is 134 mmHg, and the vapor pressure at the boiling point, which is the atmospheric pressure of 760 mmHg.

Rearrange the Clausius-Clapeyron equation to solve for the molar heat of vaporization,

ΔHvap

. The equation becomes:

ΔHvap = \frac{R \times (T1 - T2)}{(ln (\frac{P2}{P1})}

Substitute the values into the rearranged equation:

R

is 8.314 J/mol·K,

T1

is 313 K,

T2

is 273 K,

P1

is 134 mmHg, and

P2

is 760 mmHg. Calculate

ΔHvap

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