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Partial Pressure from Mole Fraction Calculator

Calculates the partial pressure of a gas in a mixture using its mole fraction and the total pressure.

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Partial Pressure of Gas i

Formula first

Overview

This equation is a direct consequence of Dalton's Law of Partial Pressures and the Ideal Gas Law. It states that the partial pressure of a specific gas () in a mixture is equal to its mole fraction () multiplied by the total pressure of the gas mixture (otal). This relationship is incredibly useful for determining the contribution of an individual gas to the overall pressure, especially when the number of moles of each gas is known.

Symbols

Variables

= Mole Fraction of Gas i, = Total Pressure, = Partial Pressure of Gas i

Mole Fraction of Gas i
Variable
Total Pressure
atm
Partial Pressure of Gas i
atm

Apply it well

When To Use

When to use: Apply this formula when you know the total pressure of a gas mixture and the mole fraction of a specific component gas, and you need to find that component's partial pressure. It's also useful for calculating mole fraction if partial and total pressures are known.

Why it matters: Understanding this relationship is vital in fields like chemical engineering for designing separation processes, environmental science for analyzing atmospheric composition, and medicine for understanding gas exchange in the body. It allows for precise quantification of individual gas contributions in complex systems.

Avoid these traps

Common Mistakes

  • Using percentage composition instead of mole fraction (convert percentage to decimal first).
  • Confusing partial pressure with total pressure.
  • Incorrectly calculating mole fraction (e.g., using mass fraction instead of mole fraction).

One free problem

Practice Problem

A gas mixture has a total pressure of 1.5 atm. If the mole fraction of Gas A is 0.2, what is the partial pressure of Gas A?

Mole Fraction of Gas i0.2
Total Pressure1.5 atm

Solve for:

Hint: Multiply the mole fraction by the total pressure.

The full worked solution stays in the interactive walkthrough.

References

Sources

  1. Atkins' Physical Chemistry (P. W. Atkins, J. de Paula)
  2. Wikipedia: Dalton's law
  3. IUPAC Gold Book: Partial pressure
  4. IUPAC Gold Book: Mole fraction
  5. Atkins' Physical Chemistry
  6. Atkins' Physical Chemistry, 11th Edition, Chapter 1: The properties of gases
  7. Wikipedia: Ideal Gas Law
  8. Chemistry: The Central Science, Brown, LeMay, Bursten — Chapter 10: Gases