Partial Pressure Calculator

The pressure that a single gas exerts in a mixture is called its partial pressure — a value used in chemistry, respiratory physiology, and industrial gas applications. Select a Calculation Method (mole fraction, ideal gas law, gas collected over water, or Henry's law), then enter the corresponding inputs like mole fraction, total pressure, moles, temperature, or gas concentration to get the partial pressure in atm, mmHg, and Pa, plus the gas's percentage composition in the mixture.

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Results

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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Frequently Asked Questions

What is Dalton's law of partial pressures?

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.

How do I calculate partial pressure using the ideal gas law?

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.

How do I calculate the partial pressure of oxygen in air?

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.

What does a high Henry's law constant mean?

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.

When should I use Henry's law for partial pressure calculations?

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.

How do I account for water vapor when collecting gas over water?

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.

What units can I use for partial pressure?

Common units include atmospheres (atm), millimeters of mercury (mmHg), torr, pascals (Pa), and kilopascals (kPa). This calculator provides results in multiple units for convenience.

Can I use partial pressure calculations for real gases?

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.