LAW OF COMBINING VOLUMES (GAY-LUSSAC'S LAW)

When gases react, they do so in a definite proportion by volume, if the volumes are measured at the same pressure and temperature. For example, in the reaction N 2 (g) + 3 H 2 (g) = 2 NH 3 (g), 3 liters of hydrogen will react with 1 liter of nitrogen to give 2 liters of ammonia if all volumes are measured at the same temperature and pressure.