How to Calculate the Mole Fraction of a Substance in the Vapor – Part 1

Vapor pressure or equilibrium vapor pressure, an indication of a liquid's thermodynamic tendency to evaporate, is the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases (solid/liquid) at a given temperature in a closed system.


Raoult's law states that the partial pressure of each component of an ideal mixture of liquids is equal to the vapor pressure of the pure component (liquid/solid) multiplied by its mole fraction in the mixture.

Dalton's law (aka Dalton's law of partial pressures) states that the total pressure exerted is equal to the sum of the partial pressures of the individual gases in a mixture of non-reacting ideal gases.

Question:

The vapor pressure of EtOH & MeOH are 44.5 & 88.7 mm Hg respectively. An ideal solution is formed at the same temperature by mixing 60 g of EtOH with 40 g of MeOH. Calculate the mole fraction of MeOH in the vapor.

Solution:



Click to enlarge the image

Χ = Mole fraction, MW = Molecular weight, p = Partial vapor pressure, p* = Partial vapor pressure of the pure component

Mole fraction in the solution and in the vapor done with ease❓ Let Chemaficionado know at mychemistryhomework@gmail.com❗

NOTE: Post updated since published

References:

(1)    Wikipedia Contributors. Chemical equilibrium. Wikipedia. https://en.wikipedia.org/wiki/Chemical_equilibrium.

(2)    Phase transition. Wikipedia. https://en.wikipedia.org/wiki/Phase_transition.

(‌3)    Wikipedia Contributors. Vapor pressure. Wikipedia. https://en.wikipedia.org/wiki/Vapor_pressure.

‌(4)    Wikipedia Contributors. Raoult’s law. Wikipedia. https://en.wikipedia.org/wiki/Raoult%27s_law.

(5)    Wikipedia Contributors. Dalton’s law. Wikipedia. https://en.wikipedia.org/wiki/Dalton%27s_law.

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