Enter your Calculation Method — mole fraction, individual gas moles, or measured conditions — then fill in Total Pressure, Temperature, Volume, or Water Vapor Pressure to find the Partial Pressure of any gas in a mixture, with results in mmHg, Pa, and as a percentage composition.
Partial Pressure
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Partial Pressure (mmHg)
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Partial Pressure (Pa)
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Percentage Composition
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Dalton's law states that the total pressure exerted by a gas mixture equals the sum of the partial pressures of each individual gas. Each gas behaves as if it alone occupies the entire container volume.
Use the formula P = nRT/V, where P is partial pressure, n is moles of the specific gas, R is the gas constant (0.08314 L·atm/mol·K), T is temperature in Kelvin, and V is volume in liters.
Oxygen has a mole fraction of approximately 0.21 in air. Multiply this by the total atmospheric pressure: P(O₂) = 0.21 × 1 atm = 0.21 atm at sea level.
A high Henry's law constant indicates that the gas has low solubility in the liquid. The gas prefers to stay in the gas phase rather than dissolve in the liquid phase.
Use Henry's law when dealing with gas-liquid equilibrium systems, such as calculating the partial pressure of dissolved gases in water or other solvents based on their concentration.
Subtract the water vapor pressure from the total measured pressure: P(gas) = P(total) - P(H₂O). Water vapor pressure depends on temperature and can be found in reference tables.
Common units include atmospheres (atm), millimeters of mercury (mmHg), torr, pascals (Pa), and kilopascals (kPa). This calculator provides results in multiple units for convenience.
These calculations assume ideal gas behavior. For real gases at high pressure or low temperature, deviations occur due to intermolecular forces and finite molecular size. Use correction factors when needed.