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

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

Calculations Review getting moles from grams? molar mass (periodic table) getting volume from moles for gas? at STP only Molar Volume (22.4 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)

CaCO3(s)  CaO(s) + CO2(g) 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)

Example 1 find moles of CO2 convert mol CO2 to mol CaCO3 convert mol CaCO3 to grams

WO3(s) + 3H2(g)  W(s) + 3H2O(l) 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)

Example 2 find moles of WO3 find moles of H2 find volume of H2

CH4(g) + 2O2(g)  CO2(g) + 2H2O(g) 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)

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