Exercise III on Finding Total Pressure: Solutions Tips

When 1 mole of methane gas (CH4) is burned at 450°C in the presence of
3 moles of oxygen gas (O2), carbon dioxide gas (CO2) and water vapors (H2O) are produced.
Assuming that all the methane is consumed in this process, calculate the following:
  1. What are the mole fractions of oxygen, carbon dioxide and water vapors in this case?
  2. If the total pressure of the mixture of gases is 2.5 atm.,
    calculate thepartial pressures of oxygen, carbon dioxide and water vapors.
Solution Tips:
In this case, the combustion reaction should be written to decide on the gases
that are present at the end of the reaction.
CH4 + 3O2 → CO2 + 2H2O + O2

At the end of reaction, 1 mole of CO2, 2 moles of water and 1 mole of O2
will be remaining → nt = 4 moles
Mole fraction of each gas is Xi = (ni/nt)
Use the determined mole fractions (Xi), the given Pt and
Dalton's equation to determine the partial pressures of the gasses.

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