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# What is Dalton's Law of Partial Pressures?

Question: What is Dalton's Law of Partial Pressures?

Dalton's law of partial pressures is used to determine the individual pressures of each gas in a mixture of gases.

Answer: Dalton's law of partial pressures states:

The total pressure of a mixture of gases is equal to the sum of the partial pressures of the component gases.

PressureTotal = PressureGas 1 + PressureGas 2 + PressureGas 3 + ... PressureGas n

An alternative of this equation can be used to determine the partial pressure of an individual gas in the mixture.

If the total pressure is known and the number of moles of each component gas are known, the partial pressure can be computed using the formula:

Px = PTotal ( nx / nTotal )

where

Px = partial pressure of gas x PTotal = total pressure of all gases nx = number of moles of gas x nTotal = number of moles of all gases This relationship applies to ideal gases, but can be used in real gases with very little error.

Dalton's Law Example Problems

Dalton's Law Calculation
Ideal Gas Example Problem - Partial Pressure

Anne Marie Helmenstine, Ph.D.