Avagadro's Law

Avagadro's Law says that for a gas at constant temperature and pressure, the volume is directly proportional to the number of moles of gas. Equal volumes of gases at the same temp and pressure have the same amount of particles. This relationship is even true for gases at low pressures. The relationship for this law is:

Source

Example: We have 12.2 L containing .50 moles of oxygen at a pressure of 1 atm and a temp of 25C. If all of the oxygen is converted to ozone at the same temp and pressure, what would be the volume?

3O2-->2O3

V1=12.2L    N1=.50mol    V2=?    N2=.33 mol

.5mol x 2mol/3mol = .33mol

12.2(.33)=V2(.5) = 8.13L