Vapor pressure measurements at various temperature values are given below. Determine the molar heat of vaporization for cyclohexane.

• A. 11,520 J/mol
• B. 72,193 J/mol
• C. 33,147 J/mol
• D. 52,968 J/mol

Answer: (C)

Verified step by step guidance

1. Convert the given temperatures from Celsius to Kelvin by adding 273.15 to each temperature value. This is necessary because the Clausius-Clapeyron equation requires absolute temperature.
2. Calculate the natural logarithm of the vapor pressure values (P) given in mmHg for each temperature.
3. Use the Clausius-Clapeyron equation in its linear form: \(\ln P = -\frac{\Delta H_{vap}}{R} \cdot \frac{1}{T} + C\), where \(\Delta H_{vap}\) is the molar heat of vaporization, \(R\) is the gas constant (8.314 J/mol·K), \(T\) is the temperature in Kelvin, and \(C\) is a constant.
4. Plot \(\ln P\) versus \(\frac{1}{T}\) and determine the slope of the resulting straight line. The slope will be equal to \(-\frac{\Delta H_{vap}}{R}\).
5. Calculate the molar heat of vaporization \(\Delta H_{vap}\) by multiplying the slope by \(-R\): \(\Delta H_{vap} = -\text{slope} \times R\).