Problem: A solution contains 50.5 g of heptane (C7H16) and 50.5 g of octane (C8H18) at 25 oC. The vapor pressures of pure heptane and pure octane at 25 oC are 45.8 torr and 10.9 torr, respectively. Assuming ideal behavior, calculate each of the following. (Note that the mole fraction of an individual gas component in an ideal gas mixture can be expressed in terms of the components partial pressure.)The vapor pressure of octane in the mixture.

FREE Expert Solution

Vapor pressure is defined as the pressure exerted by a vapor in thermodynamic equilibrium with its condensed state (solid or liquid). The equilibrium vapor pressure indicates how fast a liquid evaporates. A liquid having a high vapor pressure evaporates easily.


In this problem, we are provided with the masses of two components of a solution (heptane and octane) and their vapor pressures in pure states.


To calculate the vapor pressure of octane, we will do the following:

  • Find the mole fraction of octane in the solution
  • Find the vapor pressure of octane in the solution using its mole fraction.


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Problem Details

A solution contains 50.5 g of heptane (C7H16) and 50.5 g of octane (C8H18) at 25 oC. The vapor pressures of pure heptane and pure octane at 25 oC are 45.8 torr and 10.9 torr, respectively. Assuming ideal behavior, calculate each of the following. (Note that the mole fraction of an individual gas component in an ideal gas mixture can be expressed in terms of the components partial pressure.)

The vapor pressure of octane in the mixture.