Ch. 11 Molecular Composition of Gases If the volume of a gas in the product and reactant of a chemical equation is left at a constant temp. and pressure, then it can be shown as a ration. Avogadro’s principle – says that equal volumes of gases at the same temp. and pressure contain equal numbers of molecules.

V = kn Volume = constant x number of moles The volume of a gas is directly proportional to the number of moles of a gas. (At a constant temp. and pressure) Each gas will occupy the same volume at the same temp. and pressure  Avogadro’s principle. Standard molar volume of a gas is the volume occupied by 1 mole of a gas at STP 22.4 L

The molar mass of a gas = 1 mol. of a gas = 22.4 L of a gas at STP. Sample Problem 11-1 Sample Problem 11-2 Ideal Gas Constant  R = PV/nT Ideal gas law – relation between temp., pressure, volume, and # of moles of a gas. Sample Problems 11-3 to 11-5 Mass / molar mass = # of moles PV = mRT/M

PV = nRT or PV = mRT/M Sample Problem 11-6 Density = mass / volume P = mRT/VM D = MP / RT

Stoichiometry of Gases 1. Volume to Volume Volume A  Volume B Volume A x mol. B / mol. A = VOLUME B Sample Problem 11-7

2. Volume to Mass Volume A  Mol. A  Mol. B  mass B USE n = PV / RT to convert volume to mass Mol. A x mol. B / mol. A = mol. B x molar mass B = MASS B Sample Problem 11-8

3. Mass to Volume Mass A  Mol. A  Mol. B  Volume B Mass A / Molar mass A x mol. B / mol. A = mol. of B Use V = nRT/P to covert mol. of B into volume of B Sample Problem 11-9