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Homework Help: Thermofluids -Finding the temperature of Combustion

  1. Mar 28, 2014 #1
    1 kmol of gaseous methane (CH 4) is mixed with the correct amount of air in a closed vessel. The pressure and temperature of the mixture are 1 bar and 298 K respectively. The mixture is ignited. Estimate the adiabatic temperature of combustion.

    Answer: ~2743 K

    OK, so first I acquired the combustion equation and found the number of moles for stoichmetric conditions.

    CH4 + x[O2+ (79/21)N2] → ACO2 + BH2O +CN2

    Here by balancing the equation, I found that
    CH4 + 2[O2+ (79/21)N2] → CO2 + 2H2O +7.5N2

    Now I have a reference temperature, 298K which conveniently is 25° at 1 bar. This reads well with my steam table book for the products and reactants.

    Considering Enthalpy of reactants: ΔH0=ΔU0+pdv=∑micp(T0-Tref)

    I can find the mass of constitutes but what about the enthalpys? At the referenced temperature I find Methane, O2 and N2 to be zero which makes the equation unsolvable. Could anyone point me in the right direction at least giving me the correct steps for this.

    Many thanks

  2. jcsd
  3. Mar 28, 2014 #2
    What are the heats of formation of the reactants and of the products from your table? From these values, you should be able to calculate the heat of reaction at 1 bar and 298. What is that?

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