Multiple Choice
Methanol has a normal boiling point of 64.6°C and a heat of vaporization of 35.2 kJ/mol. What is the vapor pressure of methanol at 12.0°C?
14. Solutions
Vapor Pressure Lowering (Raoult's Law)
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Using Raoult's Law and the Clausius-Clapeyron equation, what is the vapor pressure of SiCl4 in mmHg at 31.0 °C, given that its vapor pressure is 100 mmHg at 5.4 °C and ΔHvap is 30.2 kJ/mol?
A
200 mmHg
B
250 mmHg
C
150 mmHg
D
300 mmHg
Verified step by step guidance1
First, understand that Raoult's Law is used to determine the vapor pressure of a component in a solution, but since SiCl4 is pure, we will focus on the Clausius-Clapeyron equation to find the vapor pressure at a different temperature.
The Clausius-Clapeyron equation is given by: , where and are the vapor pressures at temperatures and , respectively, is the enthalpy of vaporization, and is the gas constant.
Convert the temperatures from Celsius to Kelvin by adding 273.15 to each: = 5.4 + 273.15 K and = 31.0 + 273.15 K.
Use the given values: = 100 mmHg, = 30.2 kJ/mol (convert to J/mol by multiplying by 1000), and = 8.314 J/(mol·K).
Substitute these values into the Clausius-Clapeyron equation and solve for , the vapor pressure at 31.0 °C.
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