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Help writing chemical equation

  1. Jan 29, 2008 #1
    1. The problem statement, all variables and given/known data

    An engine is operated slightly fuel rich (phi>1). Ethylene (C2H4) and inert nitrogen (N2) are the reactants and there are 40 mol of nitrogen for every mol of ethylene. The hydrocarbons are burned over a catalyst and converted to carbon dioxide (CO2) and water vapor (H20) only. Ambient air at 298 K with a composition of 1 mol of oxygen to 4 mol of nitrogen (O2 + 4N2) is injected before the catalyst. The catalyst is maintained at 1000 K. The temperature before the injection of the catalyst is 400 K. Calculate moles of air to moles of ethylene.

    2. Relevant equations

    C2H4 + 40 N2 + (a/phi) (O2 + 4N2) --> b CO2 + c H20 (gas) + d N2, where phi is the equivalence ratio and a, b, c, and d are stoichiometric coefficients

    Hr = Hp



    3. The attempt at a solution

    For the equation I have written in (2), should O2 be included in the products? Should N2 be included in the products? I think if I can write the equation correctly, I know how to use mass balance and Hr = Hp to solve for the stoichiometric coefficient of air.

    So my major question is, is my chemical equation right? If not, how do I correct it?
     
  2. jcsd
  3. Jan 30, 2008 #2

    chemisttree

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    All you need to start is to determine the stoichiometric ratio between pure ethylene and pure oxygen. Write that equation first. Next you will determine the ratio of air (oxygen plus nitrogen) to fuel (ethylene plus nitrogen).

    Your problem gives you the information that the fuel is composed of a ratio of 40 moles Nitrogen to 1 mole of ethylene... or that ethylene is 1/41 parts of the fuel gas composition. Likewise the air contains 1 mole of oxygen (as O2) to 5 moles of air (oxygen plus nitrogen) or is 1/5 parts of the air composition.

    Can you take it from here?
     
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