Some Simple Estimating Rules Raoults and Henrys Laws

15 mol%. Air cooled to 40°F can hold only 0.83 mol% water, so the air next to the glass must reject water, normally by forming dew on the glass. 

4 SOME SIMPLE ESTIMATING RULES RAOULT S AND HENRY S LAWS  

For a pure gas the partial pressure is equal to the total pressure (because y, = 1.0 for a pure gas). For any gas mixture the sum of the partial pressures equals the total pressure, = PJlyi = P because the sum of the mol fractions is unity. The partial pressure is defined only for gases this term is not used for solids and liquids. 

An equivalent term, not as widely used but perhaps equally useful, is the partial vapor pressure of one species in a liquid, which is defined as the pure species vapor pressure of that species /), multiplied by its mol fraction in the liquid x, 

Using these definitions we can state Raoult s law (which would be better named Raoult s useful estimating approximation, because it is not a law like the laws of thermodynamics). It says that for gas-liquid equilibrium for each chemical species present, the partial pressure in the gas is equal to the partial vapor pressure in the liquid. Mathematically, Raoult s law is 

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