Worked example

0.2 O₂ at 1 atm total →0.2 atm partial.

Dalton’s Partial Pressures

Total pressure = sum of partials; partial from mole fraction.

Equation

$P_{tot}=\sum P_i,\ P_i = x_i P_{tot}$

Inline: $P_{tot}=\sum P_i,\ P_i = x_i P_{tot}$$

Variables

Symbol	Quantity	Unit	Notes
$P_tot$	total pressure	atm	—
$P_i$	partial pressure	atm	—
$x_i$	mole fraction	—	—

Conditions and limitations

Ideal gas mixture; non-reacting gases.

Rearrangements

$x_i=P_i/P_{tot}$

Dimensional check: atm ✓

Worked example

0.2 O₂ at 1 atm total →0.2 atm partial.

Steps: write equation → substitute with units → check dimensional consistency → report with correct significant figures.

Common errors

• Confusing mole fraction with mass fraction

Related resources

• gases-gas-laws topic
• Calculators — linked only when a real calculator implements this formula.
• Constants — sourced constants with version when values are required.

Sources

• NIST Physical Constants 2022 — CODATA.

Reviewed 2026-08-21 by Editorial Team; due 2027-08-21.