Dalton's Law of Partial Pressures

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Calculate the total pressure of a gas mixture by summing individual partial pressures.

Gas Mixture Components

Gas 1 Pressure

Gas 2 Pressure

Calculation Results

Enter partial pressures of individual gases to calculate the total mixture pressure

About this calculator

Overview

Dalton's Law of Partial Pressures states that the total pressure of a gas mixture equals the sum of the partial pressures of its individual components. This fundamental principle explains how gases behave in mixtures and has critical applications in respiratory physiology, diving, and atmospheric science. The law assumes ideal gas behavior and no chemical interactions between components.

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Pro Tips

Units must be consistent: all pressures in atm, kPa, torr, or mmHg—mixing units gives wrong results!
Partial pressure relates to mole fraction: Pᵢ = Xᵢ × Pₜₒₜₐₗ, where Xᵢ = moles of gas i / total moles.
The law assumes ideal gases—no molecular interactions or chemical reactions between components.
For water vapor above liquid, total pressure = vapor pressure + atmospheric pressure (if open system).
At constant volume and temperature, adding gas increases total pressure by exactly its partial pressure.
Real gases deviate at high pressures; van der Waals corrections needed for accurate modeling.
In closed systems, removing one gas doesn't change others' partial pressures—total pressure drops proportionally.

Fun Facts

"John Dalton discovered this law in 1801 while studying water vapor pressure and atmospheric composition—long before atomic theory!"
"At Everest's summit (8,848m), atmospheric pressure drops to ~0.3 atm; oxygen's partial pressure falls to ~0.06 atm, causing severe hypoxia."
"Scuba divers use Dalton's Law to prevent 'the bends'—nitrogen narcosis from increased N₂ partial pressure at depth."
"The law explains why you can breathe through a straw in a glass of water—the total pressure equals atmospheric pressure."
"Medical oxygen masks deliver pure O₂ at higher partial pressure to force more oxygen into blood despite lower total pressure."
"Dalton's Law powers gas chromatography, separating compounds based on their vapor pressures and interactions with stationary phases."
"The law applies to both homogeneous mixtures (gases mixed uniformly) and heterogeneous systems (like water vapor above liquid)."
"Atmospheric air is 78% N₂, 21% O₂, 1% Ar—giving partial pressures of ~0.79 atm N₂ and ~0.21 atm O₂ at sea level."
"Hyperbaric chambers use Dalton's Law to deliver oxygen at 2-3 atm partial pressure for treating carbon monoxide poisoning."
"The law fails at high pressures where gas molecules interact significantly, requiring corrections for real gas behavior."

Formula: Pₜₒₜₐₗ = P₁ + P₂ + ... + Pₙ