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
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1
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.