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 = knVolume = 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

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

PV = nRT or PV = mRT/M

Sample Problem 11-6

Density = mass / volume

P = mRT/VM

D = MP / RT

Stoichiometry of Gases1. Volume to Volume Volume A Volume B

Volume A x mol. B / mol. A = VOLUME B

Sample Problem 11-7

2. Volume to MassVolume A Mol. A Mol. B mass

BUSE 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 VolumeMass 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