Partial Pressure The partial pressure of a gas in a mixture is the pressure that the gas would have if it alone occupied the volume occupied by the whole mixture. If a mixture of gases contains 3 different gases then the total pressure will equal the 3 partial pressure added together P =p1 + p2 + p3 partial pressure = mole fraction x total pressure of gas 1 of gas 1 mole fraction = number of moles of a gas total number of moles of all gases For a 3 part mixture x1 = y1 y1+y2 +y3 Example : A mixture contains 0.2 moles N2 , 0.5 moles O2 and 1.2 moles of CO2. If the total pressure is 3kPa. What are the partial pressures of the 3 gases?If a reaction contains gases an alternative equilibrium expression can be set up using the partial pressures of the gases instead of concentrations

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3.1.10 Equilibrium constant K p for homogeneous systems (A-level only)

Students should be able to:

• derive partial pressure from mole fraction and total pressure