# At 20 degrees C the vapor pressure of toluene is 22 mm-Hg and that of benzene is 75 mm-Hg. Assume...

## Question:

At {eq}20 ^\circ C{/eq}, the vapor pressure of toluene is 22 mm-Hg and that of benzene is 75 mm-Hg. Assume an ideal solution, equimolar in benzene and toluene. At {eq}20 ^\circ C{/eq}, what is the mole fraction of benzene in the vapor in equilibrium with this solution?

## Raoult's Law:

When given a vapor that contains both toluene and benzene, we can use the following expression for the vapor pressure of the given solution:

{eq}\displaystyle P=\chi_{B}P_{B}+\chi_{T}P_{T}{/eq}, where:

• {eq}P_{B}, \ P_{T}{/eq} are partial pressures of the substance benzene and toluene.
• {eq}\chi_{B}, \chi_{T}{/eq} are mole fractions of the substance benzene and toluene.

The mole fraction of any component of the solution is represented as:

{eq}\displaystyle \chi_{B}=\frac{n_B}{n}{/eq}, where:

• n is the value of the total number of moles of the solution.

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We are given the following data:

• The value of the temperature of the given system is {eq}T=20 ^\circ C{/eq}.
• The value of the toluene's vapor...

Vapor Pressure: Definition, Equation & Examples

from

Chapter 19 / Lesson 6
21K

This lesson explains the definition of vapor pressure, describes how vapor pressure changes as a function of temperature according to the Clausius-Clapeyron equation, and shows how to determine the vapor pressure of a single component in a mixture of liquids using Raoult's Law.