The vapor pressures of pure hexane and pure heptane at 25 °C are 151.4 mmHg and 45.62 mmHg respectively.A solution contains 0.800 mol fraction n-hexane and 0.200 mol fraction n-heptane.What is the composition of the vapor in equilibrium with this solution at 25 °C?
A)80.0% hexane,20.0% heptane
B)50.0% hexane,50.0% heptane
C)77.0% hexane,23.0% heptane
D)45.0% hexane,55.0% heptane
E)93.0% hexane,7.0% heptane

Question

Quizplus · Accepted Answer

The vapor composition is determined by Raoult's Law. The partial pressure of hexane is 0.800 * 151.4 mmHg = 121.12 mmHg, and for heptane, it is 0.200 * 45.62 mmHg = 9.124 mmHg. The total pressure is 121.12 + 9.124 = 130.244 mmHg. The mole fraction of hexane in the vapor is 121.12 / 130.244 = 0.929 or 92.9%, and for heptane, it is 9.124 / 130.244 = 0.070 or 7.0%.

The Vapor Pressures of Pure Hexane and Pure Heptane at 25