Dalton Partial Pressure Calculator
Find each gas's partial pressure in a mixture from its moles and the total pressure, using Dalton's law.
How it works
xᵢ = nᵢ / n_total · Pᵢ = xᵢ · P_total (Dalton's law)
Dalton's law of partial pressures says each gas in a mixture exerts the pressure it would if it alone occupied the container, and the total pressure is the sum of those partial pressures. Each partial pressure equals the total pressure times that gas's mole fraction, so the composition by moles directly sets the pressure split.
Worked example
A mixture of 2 mol A and 3 mol B (5 mol total) at 5 atm: mole fraction of A is 2/5 = 0.4, so P_A = 0.4 × 5 = 2 atm and P_B = 0.6 × 5 = 3 atm.
Sources: Dalton's law — Wikipedia
Frequently asked questions
What is a mole fraction?
It is the moles of one gas divided by the total moles of all gases. Mole fractions always sum to 1, and each one multiplied by the total pressure gives that gas's partial pressure.
Does Dalton's law need ideal gases?
It assumes ideal behaviour and no chemical reaction between the gases. That holds well at ordinary pressures and temperatures.
Can I use volumes or percentages instead of moles?
For ideal gases, volume percent equals mole percent, so you can enter relative volumes or percentages and get the same fractions.
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