2. Objectives: State the law of combining volumes. State Avogadro’s law and explain its significance. Define standard molar volume of a gas, and use it to calculate gas masses and volumes. Use standard molar volume to calculate the molar mass of a gas.
3. Molecular Composition of Gases Volume-mass relationship of gases Hydrogen Gas + Oxygen gas Water Vapor 2 L 1 L 2 L 2 Volumes 1 Volume 2 Volumes Gay Lussac’s Law of Combining Gas Volumes At constant temperature and pressure, the volumes of gaseous reactants and products can be expressed as ratios of small whole numbers.
4. Avogadro’s Law Equal Volumes of gases at the same temperature and pressure contain equal numbers of molecules. How does it work! Hydrogen Gas + Chlorine gas Hydrochloric Acid H2 Cl2 2HCl 1 Volume 1 Volume 2 Volumes 1 Molecule 1 Molecule 2 Molecules 1 Mol 1 Mol 2 Mol V = kn Direct Relationship n = amount of gas
5. Molar Volume of Gas Recall 1 mol = 6.022 x 10 23 molecules 1 mol O2 = 6.022 x 10 23 molecules O2 = 32.00 g O2 1 mol H2 = 6.022 x 10 23 molecules H2 = 2.02 g H2 Standard Molar Volume of gases Volume occupied by 1 mol of a gas at STP At STP, 1 mol of any gas = 22. 4 L
6. Sample Problem 1 A chemical reaction produces 0.0680 mol of oxygen gas. What volume in liters is occupied by this gas sample at STP? 22.4 L O2 0.0680 mol O2 x = 1.52 L O2 1 mol O2 Sample Problem 2 A chemical reaction produced 98.0 mL of sulfur dioxide gas, SO2, at STP. What was the mass (in grams) of the gas produced? 98.0 mL SO2 1 L SO2 1 mol SO2 64.07 g SO2 x x x 1000 mL SO2 22.4 L SO2 1 mol SO2 = 0.280 g O2
