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Partial pressure

In a gas mixture each gas contributes its own pressure, the partial pressure, as if it were alone in the container. The total pressure is the sum of the partial pressures. A partial pressure is the total pressure times the mole fraction.

ptot=p1+p2+…p_{tot} = p_1 + p_2 + \dotsDalton's law
pi=xi ptotp_i = x_i\,p_{tot}partial pressure from mole fraction

Symbols

pip_ipartial pressure of gas iPa
xix_imole fraction of gas i

Example

Air with 21 % oxygen at 101 kPa:

pO2=0.21⋅101≈21p_{O_2} = 0.21\cdot 101 \approx 21 kPa.

The mole fractions in a mixture always add up to 1.
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← The combined gas law

Part of General Chemistry: Gas laws.