Dalton's Law of Partial Pressures Calculator

Dalton's Law states that the total pressure of a gas mixture equals the sum of each gas's individual partial pressure — the pressure each gas would exert if it occupied the container alone. Use the Dalton's Law of Partial Pressures Calculator by selecting a calculation mode: enter moles, temperature, and volume to find individual partial pressures; enter known partial pressures directly to sum them; or use a mole fraction and total pressure to find a single gas's partial pressure.

Calculation Mode *

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Optional third gas

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atm
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Results

Total Pressure

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Partial Pressure Gas 1

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Partial Pressure Gas 2

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Partial Pressure Gas 3

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Total Moles

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Frequently Asked Questions

What is Dalton's law of partial pressures?

Dalton's law states that the total pressure of a gas mixture equals the sum of the partial pressures of each individual gas. Each gas behaves as if it were alone in the container.

How do I calculate partial pressure from moles?

Use the ideal gas law: P₁ = (n₁ × R × T) / V, where n₁ is moles of gas 1, R is the gas constant (0.08206 L·atm/mol·K), T is temperature in Kelvin, and V is volume in liters.

How do I calculate partial pressure of oxygen?

For oxygen in air, multiply the total pressure by oxygen's mole fraction (0.21). For example, at 1 atm total pressure, oxygen's partial pressure is 0.21 atm.

What is mole fraction and how does it relate to partial pressure?

Mole fraction is the ratio of moles of one gas to total moles (x₁ = n₁/ntotal). Partial pressure equals mole fraction times total pressure: P₁ = x₁ × Ptotal.

When is Dalton's law most accurate?

Dalton's law is most accurate for ideal gases at low pressures and high temperatures, where gas molecules don't interact significantly with each other.

How do I convert between pressure units?

Common conversions: 1 atm = 101,325 Pa = 101.325 kPa = 1.01325 bar = 760 mmHg. Use these factors to convert between different pressure units.

Can I use Dalton's law for gas mixtures over water?

Yes, but you must account for water vapor pressure. The dry gas pressure equals total pressure minus water vapor pressure: Pgas = Ptotal - PH₂O.

What happens if I have more than three gases in my mixture?

Dalton's law applies to any number of gases. Simply sum all individual partial pressures to get the total pressure, regardless of how many gases are present.