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Homework Help: Chemical Process Analysis - Mole Flow Rate

  1. Mar 30, 2013 #1
    1. The problem statement, all variables and given/known data

    120 mol/min of Propane (C3H8) is burned in the presence of air (21% O2 and 79% N2) in a furnace, two reactions occur:
    Complete Combustion: 67%, propane is burned to CO2 and H2O
    Incomplete Combustion: 18%, propane is burned to CO and H2O

    Oxygen is supplied at 70% excess.

    2. Relevant equations

    %Excess = (In - Req'd *100%)/Req'd

    Complete Combustion: 2C3H8 + 10O2 -> 6O2 + 8H2O
    Incomplete Combustion: 2C3H8 + 7O2 -> 6O + 8H2O

    3. The attempt at a solution

    So for the complete combustion....
    120 Moles C3H8 * 5 Required Moles of O2 * 67% Required for Complete Combustion = 402 Moles
    So for the incomplete combustion....
    120 Moles C3H8 * 3.5 Required Moles of O2 * 18% Required for Complete Combustion = 75.6 Moles

    Total of 477.6 Moles required
    Using %Excess Formula, you get, In = 477.6 * 0.7 + 477.6 = 811.92 Moles...

    HOWEVER, my lecturer simply had:

    120moles/min * 1.7 * 5/1 = 1020 moles of O2.

    I'm extremely clueless to as how he got that.

  2. jcsd
  3. Mar 30, 2013 #2
    1. State what is "Kauzmann Paradox" and provide your own explanation (or solution) for the paradox and derive a unique explanation using different approaches.

    2. If you observe a phase transition phenomenon in your own experiment, how to determine the whether the transition is binodal or spinodal?

    3. Explain the origin of the friction when an elastic rubber ball is bouncing on a ground made of a crystalline material using an entropy analysis.

    Thanks in Advance
  4. Mar 30, 2013 #3
    I think that you missed a very important bit of information.

    Complete Combustion: 67%, propane is burned to CO2 and H2O
    Incomplete Combustion: 18%, propane is burned to CO and H2O

    This only accounts for 85% of the propane, so your calculations exclude the oxygen used in 15% of the reactions.

    The professor took the flow rate of the propane, multiplied by the 70% excess (1.7) and then by the molar ratio (from the balanced chemical equation for complete combustion) (5 moles of O2 over 1 mole of propane).

    The answer should be 1020 moles of O2 per minute.
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