Dalton's Law

A barometer that measures atmospheric pressure
is used to help forecast the weather

The atmosphere surrounding Earth is composed of air. The most important gas in the atmosphere is oxygen. As you may know, oxygen only makes up twenty-one percent of the air you breathe. Nitrogen is found in the highest abundance at seventy-eight percent. The final one percent of gases is a combination of many other gases - so many that it might take the rest of this page to list them all.

Different gases have a different molecular weight and density. Dalton’s Law will help you to understand that in a mixture of gases, all of the individual gases have varying pressures, like the example of the atmosphere. The sum of all the varying pressures from the different gases in the atmosphere is needed to determine atmospheric pressure. In this topic, you will investigate Dalton’s Law of Partial Pressures.

Essential Question

• How is Dalton’s Law of Partial Pressures used to calculate the total pressure of a container that holds mixed gases?