Molecular Composition of Gases Volume-Mass Relationships of Gases

Objectives: 1.State Avogadro’s Law and explain its significance. 2.Define the standard molar volume of a gas and use it to calculate gas mass and volume. 3.Use molar volume to calculate the density and molar mass of a gas at STP.

Volumes of Reacting Gases Gay-Lussac’s Law of Combining Volumes of Gases 1808 – At constant temperature and pressure, the volumes of gaseous reactants and products can be expressed as ratios of small whole numbers Hydrogen + Oxygen  water vapor 2 L 1 L 2 L Nitrogen + Hydrogen  ammonia 1 L 3 L 2 L

Avogadro’s Law Equal volumes of gases at the same temperature and pressure contain equal numbers of molecules. Explained Gay-Lussac’s observations. Remember:

Avogadro’s Law N H 2  2 NH 3 1 L 3 L 2 L 1 molecule 3 molecules 2 molecules 1 mol 3 mol 2 mol

Avogadro’s Law 1.Ozone can be formed by the following reaction: 3 O 2  2 O 3 If both gases are at constant temp. and pressure… a)How many molecules of ozone are formed from the reaction of 24 oxygen molecules? b)How many moles of oxygen are required to produce 24 moles of ozone? c)How many Liters of ozone are produced from 12 L of oxygen 2.How many liters of chlorine at STP will react with 35 L O 2 at STP? Use the following reaction. 2 Cl O 2  2 Cl 2 O 7

Molar Volume of Gases At STP……. 1 mole of a gas = 22.4 L This conversion factor can be used with molar mass to relate mass, moles, and volume of a gas.

Molar Volume of Gases 1.At STP, what is the volume of 7.08 mol of nitrogen gas? 2.A sample of hydrogen gas occupies 14.1 L at STP. How many moles of the gas are present? 3.What is the mass of 1.33 x 10 4 mL of oxygen gas at STP? 4.What is the volume of 77.0 g of nitrogen dioxide gas at STP 5.At STP, 3 L of chlorine is produced during a chemical reaction. What is the mass of this gas?