Panel 7: Mixtures of Gases

In a gas mixture, each different gas exerts its own partial pressure, and the total pressure is the sum of the partial pressures. (This rule is known as Dalton's law of partial pressures.) In the example shown on the screen, you might think of the red particles as oxygen molecules and the blue particles as nitrogen.

The ideal gas law applies to mixtures in several different ways. You can calculate the partial pressure of each gas using the ideal gas law for each gas separately. The total pressure is the sum of the partial pressures. That calculation is shown on the upper right-hand side of your screen.

On the other hand, if you insert the total number of moles of gas (all kinds added together), the ideal gas law gives you the total pressure in the system. That calculation is shown on your lower right. You can see that it gives the same answer as adding the partial pressures, as it should.