Multiple Choice
The vapor pressure of SiCl4 is 100 mmHg at 5.4 °C, and the normal boiling point is 57.7 °C. What is the enthalpy of vaporization (ΔHvap) for SiCl4 in kJ/mol?
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
Using the Clausius-Clapeyron equation, what is the enthalpy of vaporization (ΔHvap) for the reaction A(l) ⇌ B(g) if the equilibrium constant K is 3.2 × 10^(-3) at 0 °C and 8.1 × 10^(-3) at 50 °C?
A
ΔHvap = 31.2 kJ/mol
B
ΔHvap = 24.5 kJ/mol
C
ΔHvap = 18.7 kJ/mol
D
ΔHvap = 42.0 kJ/mol
Verified step by step guidance1
Understand the Clausius-Clapeyron equation, which is used to relate the change in vapor pressure with temperature to the enthalpy of vaporization. The equation is: , where P is the pressure, T is the temperature, R is the gas constant, and ΔHvap is the enthalpy of vaporization.
Convert the equilibrium constants to pressures using the relation between K and P for the reaction A(l) ⇌ B(g). Since K is proportional to the pressure of B(g), you can use the given values of K as proxies for pressure at the respective temperatures.
Use the natural logarithm of the equilibrium constants at the two temperatures to find the change in ln(P) with respect to temperature. Calculate , where K1 and K2 are the equilibrium constants at 0 °C and 50 °C respectively.
Determine the change in temperature in Kelvin. Convert the temperatures from Celsius to Kelvin by adding 273.15 to each temperature. Calculate the difference: .
Rearrange the Clausius-Clapeyron equation to solve for ΔHvap: . Use the gas constant R = 8.314 J/(mol·K) to calculate ΔHvap.
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