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Homework Help: Heat of combustion

  1. Dec 3, 2013 #1


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    Gold Member

    1. The problem statement, all variables and given/known data

    Given the following enthalpies calculate the molar heat of combustion of C2H2.

    Heat of formation of liquid water: -285.8 kJ/mol
    Heat of formation of C2H2 (gas): -26.7 kJ/mol
    Heat of formation of CO2 (gas): -393.5 kJ/mol

    2. Relevant equations

    Heat of combustion is heat of products minus heat of reactants.

    3. The attempt at a solution

    I balance the equation and I get:

    2C2H2 + 5O2 => 4CO2 + 2H2O

    The sum of the heat of the products minus the sum of the heat of the reactants, with the heat of oxygen being 0, is 2092.2 kJ.

    Since there are two moles of C2H2 being combusted we must divide by 2 and we get 1046.1 kJ/mol.

    Since this is combustion this is an exothermic reaction and so the heat of combustion is -1046.1 kJ/mole.

    Is this correct?
  2. jcsd
  3. Dec 4, 2013 #2


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    Staff: Mentor

    Logic is sound.
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