Avogadros Law The Amount-Volume Relationship

In 1811, the Itahan scientist Amedeo Avogadro proposed that equal volumes of different gases contain the same number of particles (molecules or atoms) at the same temperature and pressure. This hypothesis gave rise to Avogadro s law, which states that the volume of a sample of gas is directly proportional to the number of moles in the sample at constant temperature and pressure  

As with the other gas laws, we can compare two sets of conditions using Avogadro s law where n and Fboth change at constant pressure and temperature and write 

The balanced equation reveals the ratio of combination of reactants in terms of moles [Ml Section 3.4]. However, because the volume of a gas (at a given temperature and pressure) is directly proportional to the number of moles, the balanced equation also reveals the ratio of combination in terms of volume. Thus, if we were to combine three volrrmes (liters, milliliters, etc.) of hydrogen gas with one volrrme of rritrogen gas, assuming they react completely according to the balanced eqrration, we wotrld expect two volumes of ammorria gas to be produced (Figitre 11.11). The ratio of combination of H2 arrd N2 (and production of NH3), whether expressed in moles or rmits of volume, is 3 1 2. 

2NO(g) + 02(g)------- 2N02(g), what volume of NO2 will be produced (Assume that the reactants 

Strategy Apply Avogadro s law to determine the volume of a gaseous product. 

Avogadro s law makes it possible to predict the volumes of gaseous reactants and products. Consider the reaction of H2 and N2 to form NH3  

Think About It Remember that the coefficients in balanced chemical equations indicate ratios in molecules or moles. Under conditions of constant temperature and pressure, the volume of a gas is proportional to the number of moles. Therefore, the coefficients in balanced equations containing only gases also indicate ratios in liters, provided the reactions occur at constant temperature and pressure. 

---