Ch. 11 Molecular Composition of Gases

1. 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.

2. 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

3. ` • 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

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

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

6. 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

7. 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