Multiple Choice
Using the two-point form of the Clausius-Clapeyron equation, calculate the vapor pressure of methanol at 12.0°C given its normal boiling point is 64.6°C and its heat of vaporization is 35.2 kJ/mol.
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13. Liquids, Solids & Intermolecular Forces
Clausius-Clapeyron Equation
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Join thousands of students who trust us to help them ace their exams!Watch the first videoMultiple Choice
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
Verified step by step guidance1
Convert the temperature values from degrees Celsius to Kelvin by adding 273.15 to each temperature value.
Use the Clausius-Clapeyron equation, which is ln(P2/P1) = -ΔHvap/R * (1/T2 - 1/T1), where P1 and P2 are the vapor pressures at temperatures T1 and T2, ΔHvap is the molar heat of vaporization, and R is the ideal gas constant (8.314 J/mol·K).
Select two data points from the table, for example, (T1 = 0°C, P1 = 28 mmHg) and (T2 = 20°C, P2 = 78 mmHg), and convert the temperatures to Kelvin.
Substitute the values of P1, P2, T1, and T2 into the Clausius-Clapeyron equation and solve for ΔHvap.
Repeat the calculation using another pair of data points to verify the consistency of the calculated ΔHvap value.
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