•Remember according to Avogadro’s law, one mole of any gas will occupy the same volume as one mole of any other gas at the same temperature regardless of mass.•The volume occupied by one mole of a gas at STP is known as the standard molar volume of a gas. •It has been found to be 22.41410 L (22.4 L).•This can be used as a conversion factor.

•Consider the reaction of carbon monoxide with oxygen to give carbon dioxide.

2CO(g)2 molecules2 mol2 volumes

+ O2(g)1 molecule1 mol1 volume

→ 2CO2(g)2 molecules2 mol2 volumes

•For gaseous reactants or products, the coefficients not only indicate molar amounts and mole ratios but also reveal volume ratios.

•The rates of effusion and diffusion depend on the relative velocities of gas molecules.•The velocity of a gas varies inversely with the square root of its molar mass. •Lighter molecules move faster than heavier molecules at the same temperature.•Graham’s law of effusion states that the rates of effusion of gases at the same temperature and pressure are inversely proportional to the square roots of their molar masses.

A

B

M

M

B ofeffusion of rate

A ofeffusion of rate