# What is Avogadro's Law?

##### 1 Answer

Avogadro's law states that, at the same temperature and pressure, equal volumes of all gases have the same number of molecules.

#### Explanation:

Another statement is, "Volume is directly proportional to the number of moles."

The volume increases as the number of moles increases. It does not depend on the sizes or the masses of the molecules.

We can rewrite this as

Equal volumes of hydrogen, oxygen, or carbon dioxide contain the same number of molecules.

STP is 0 °C and 1 bar.

One mole of an ideal gas occupies 22.71 L at STP. Thus, its *molar volume* at STP is 22.71 L

**Example Problem**

A 6.00 L sample at 25.0 °C and 2.00 atm contains 0.500 mol of gas. If we add 0.250 mol of gas at the same pressure and temperature, what is the final total volume of the gas?

**Solution**

The formula for Avogadro's law is: