Boyle's, Charles's, Gay-Lusaac's and Avogadro's Gas Law for AP Chemistry (page 2)

By — McGraw-Hill Professional
Updated on Feb 9, 2011

Volume–Amount Relationship: Avogadro's Law

In all the gas law problems so far, the amount of gas has been constant. But what if the amount changes? That is where Avogadro's law comes into play.

If a container is kept at constant pressure and temperature, and you increase the number of gas particles in that container, the volume will have to increase in order to keep the pressure constant. This means that there is a direct relationship between the volume and the number of moles of gas (n). This is Avogadro's law and mathematically it looks like this:

    V/n = ka   or   V1/n1 = V2/n2

We could work this into the combined gas law, but more commonly the amount of gas is related to the other physical properties through another relationship that Avogadro developed:

      1 mol of any gas occupies 22.4 L at STP
    [Standard Temperature and Pressure of 0°C (273 K) and 1 atm]

The combined gas law and Avogadro's relationship can then be combined into the ideal gas equation, which incorporates the pressure, volume, temperature, and amount relationships of a gas.

Practice problems for these concepts can be found at:

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