Partial Pressure Calculator
Find a gas's partial pressure from its mole fraction.
Dalton's law: each gas contributes pressure in proportion to its mole fraction.
How the Math Works
The Partial Pressure Calculator uses Dalton's Law of Partial Pressures, which states that in a mixture of non-reacting gases, the total pressure is the sum of the individual partial pressures of each gas. The formula P_partial = mole fraction × total pressure allows us to calculate the contribution of a single gas to the overall pressure. The mole fraction represents the proportion of that specific gas's moles relative to the total moles in the mixture, making it a dimensionless value between 0 and 1. When you multiply this fraction by the total pressure of the gas mixture, you obtain the partial pressure exerted by that particular gas alone.
Practical Applications
To use this calculator, first determine the number of moles of the gas of interest and divide it by the total number of moles in the mixture to find the mole fraction. Next, measure or obtain the total pressure of the entire gas mixture using a pressure gauge or from experimental data. Input these values into the calculator: mole fraction times total pressure. For example, if oxygen constitutes 0.21 moles in a mixture of 1.00 mole total gases under 1 atmosphere pressure, the partial pressure of oxygen is 0.21 atm. This calculation is essential in chemistry labs, chemical engineering, and environmental science.
Day-to-Day Use
Understanding partial pressures helps explain many everyday phenomena. It's why scuba divers must carefully manage their air supply at different depths—gas partial pressures change with environmental pressure, affecting oxygen toxicity and nitrogen narcosis. Your body uses partial pressure differences to exchange oxygen and carbon dioxide when you breathe. Weather systems rely on partial pressure concepts, as does the operation of air conditioning units and refrigeration systems in your home. Even the quality of the air you breathe indoors depends on understanding how different gas components contribute to total atmospheric pressure.
Worked example
Oxygen (0.21) at 1 atm → 0.21 atm.
FAQ
Sum of partials?
Equals the total pressure (Dalton's law).