A partial molar property of a component in a mixture may be either greater than

Question

A partial molar property of a component in a mixture may be either greater than or less than the corresponding pure component molar property. Furthermore, the partial molar property may vary with composition in a complicated way. Let's study in more detail a very popular mixture: ethanol and water. Compute the the partial molar volumes, and the partial molar enthalpies of ethanol and water in an ethanol-water mixture. Below are some experimental data on this mixture provided by the International Critical Tables.

Explanation / Answer

a) Let us say the mixture is 50% by weight (100 g of solution)

Moles of water = Mass / Mol wt = 50 /1 8 = 2.78

Moles of ethanol = 50 / 46 = 1.087

nethanol / mole of water = 1.087 / 2.78 = 0.391

Mass per 1 mole of water = 0.391 x 46 + 1X 18 = 35.986

Volume = Mass / Density = 35.968 / 0.9138 = 39.38 mL / mole

b) Mole % of water = 10%

So nwater = 0.1 / 0.9 = 0.111

Partial molar enthalpy = 0.092 / 0.111= 0.8288 KJ / mole

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