Ch. 11: Molecular Composition of Gases

1. Ch. 11: Molecular Composition of Gases 11.3: Stoichiometry of Gases

2. Stoichiometry of Gases • Remember that coefficients give you • ratio of moles • ratio of molecules • ratio of volumes even if the gases have different conditions only when gases are all at same T and P

3. Calculations Review • getting moles from grams? • molar mass (periodic table) • getting volume from moles for gas? • at STP only • Molar Volume (224. L = 1 mol) • any conditions • Ideal Gas Law (PV = nRT, solve for V) • getting from one type gas to new gas • mole ratio (coefficients in equation)

4. Example 1 • Calcium carbonate can be heated to make calcium oxide according to the following equation: CaCO3(s)  CaO(s) + CO2(g) • How many grams of CaCO3 must be decomposed to make 5.00 L of CO2 at STP? • volume of CO2 moles CO2 (molar volume) • moles CO2  moles CaCO3 (mole ratio) • moles CaCO3  grams CaCO3 (molar mass)

5. Example 1 • find moles of CO2 • convert mol CO2 to mol CaCO3 • convert mol CaCO3 to grams

6. Example 2 • Tungsten is made industrially by: WO3(s) + 3H2(g)  W(s) + 3H2O(l) • How many liters of hydrogen gas at 35°C and 0.980 atm are needed to react completely with 875 g WO3? • grams of WO3 moles WO3 (molar mass) • moles WO3  moles H2 (mole ratio) • moles H2  volume H2 (PV = nRT)

7. Example 2 • find moles of WO3 • find moles of H2 • find volume of H2

8. Example 3 • Combustion of methane gas produces carbon dioxide gas and water vapor. CH4(g) + 2O2(g)  CO2(g) + 2H2O(g) • If the reaction produces 213 L of CO2 at STP, what volume of O2 must have been used at 23C and 0.89 atm? • volume of CO2 moles CO2 (molar volume) • moles CO2  moles O2 (mole ratio) • moles O2  volume O2 (PV = nRT)

9. Example 3 • find moles of CO2 • convert mol CO2 to mol O2 • Find volume of O2