Gas Stoichiometry

You know the drill… Write the balanced chemical equation State your givens Make sure your units are consistent (i.e. convert to Kelvin, kPa, etc.) Use mole ratios to solve

Example 1: Volume-to-Volume A catalytic converter in the exhaust system of a car uses oxygen (from the air) and a catalyst to convert poisonous carbon monoxide to carbon dioxide. If temperature and pressure remain constant, what volume of oxygen is required to react with 65.0 L of carbon monoxide produced during a road trip? Law of Combining Volumes: At a constant T and P, volumes of gaseous reactants and products react in whole-number ratios. 2 CO(g) + O2(g)  2 CO2(g) 65.0 L V = 65.0 L X 1 molO2 2 molCO = 32.5 L  The volume of oxygen required is 32.5 L

Example 2: Mass-to-Volume PV = nRT What volume of carbon dioxide is produced when 6.40 g of methane gas, CH4, reacts with excess oxygen? All gases are at 35.0˚C and 100.0 kPa. T = 308.15 K R = 8.314 kPa·L/mol·K CH4(g) + 2 O2(g)  CO2(g) + 2 H2O(g) m = 6.40 g MM = 16.05 g/mol n = 6.40 g X 1 mol 16.05 g n = 0.3988 mol n = 0.3988 molCH4 X 1 molCO2 1 molCH4 n = 0.3988 molCO2 PV = nRT V = nRT P V = (0.3988 mol)(8.314 kPa·L·mol-1·K-1)(308.15 K) 100.0 kPa V = 10.2 L

Example 3: Volume-to-Mass PV = nRT What mass of sodium azide, NaN3(s), is required to produce the 67.0 L of nitrogen gas that is needed to fill a car’s airbag? Assume a temperature of 32˚C and a pressure pf 105 kPa T = 305.15 K R = 8.314 kPa·L/mol·K 2 NaN3(s)  2 Na(s) + 3 N2(g) n = 2.774 molN2 X 2 molNaN3 3 molN2 n = 1.849 molNaN3 MM = 65.02 g/mol m = 1.849 mol X 65.02 g 1 mol m = 120.22 g m = 1.2 X 102 g V = 67.0 L PV = nRT n = PV RT n = (105 kPa)(67.0 L) (8.314 kPa·L·mol-1·K-1)(305.15 K) n = 2.774 mol