Gas Stoichiometry

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Gas Stoichiometry
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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

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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
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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 35.0C and 100.0 kPa.

T 308.15 K R 8.314 kPaL/molK
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 kPaLmol-1K-1)(308.15 K)
100.0 kPa V 10.2 L
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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 cars airbag? Assume a
  temperature of 32C and a pressure pf 105 kPa

T 305.15 K R 8.314 kPaL/molK
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 kPaLmol-1K-1)(305.15 K) n 2.774 mol