Dalton's Law Calculator
Partial pressures from mole fractions.
Work out Dalton's Law. Partial pressures from mole fractions. Shows the working, not just the answer.
Partial pressure of A (atm)
1
Total 4 atm across 3 gases
Each gas exerts the pressure it would exert alone in the same volume, and those add to the total. So a partial pressure is just the mole fraction times the total — the identity of the gas is irrelevant, which is the same indifference that makes colligative properties work. This is why a diver's gas mix is specified by partial pressure rather than percentage: at depth the percentage is unchanged while the partial pressure is what becomes toxic.
How the Dalton's Law Calculator works
Each gas exerts the pressure it would exert alone in the same volume, and those add to the total. So a partial pressure is the mole fraction times the total, and the identity of the gas is irrelevant.
Also known as: partial pressure calculator · dalton's law of partial pressures · gas mixture pressure calculator · how to calculate partial pressure
Frequently asked questions
What is Dalton's law?
The total pressure of a gas mixture is the sum of the partial pressures of its components, each of which is its mole fraction times the total.
Why do divers care about partial pressure rather than percentage?
Because toxicity depends on partial pressure, not proportion. Air stays 21% oxygen at every depth, but at 60 metres that is a partial pressure high enough to be dangerous.
Does the type of gas matter?
No. Dalton's law treats every gas identically, which is the same indifference that makes colligative properties work — only the number of particles counts.
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