Partial Pressure & Vapor Pressure

Pi = Ptotal = P*
Since our system contains a pure substance at equilibrium, the vapor pressure of species i, P*(Tsat), equal to the total pressure and therefore :
Pi = (yi) (Ptotal) = Ptotal
For a pure substance there is only one species and, therefore, the vapor mole fraction is one (yi = 1). So, the partial pressure of species i is equal to the total pressure :
= the partial pressure of species i
= the vapor phase mole fraction of species i
= the total pressure

Partial Pressure

The FRACTION of the total pressure in a gas phase due to the presence of one particular substance.
In an ideal gas mixture :
Ptotal V = ntotal R T
Pi V = ni R T
Mole fraction related to partial pressure
Pi = (yi) (Ptotal)
Where :




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Ch 2, Lesson D, Page 2 - Partial Pressure & Vapor Pressure