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Homework Help: KJ per hydrocarbon "empirical formula unit"

  1. Oct 15, 2014 #1
    1. The problem statement, all variables and given/known data
    A sample of a hydrocarbon is combusted completely in O2(g) to produce 19.65gCO2(g), 4.023gH2O(g), and 280kJ of heat.

    Calculate the value of ΔH∘f per empirical-formula unit of the hydrocarbon.

    2. Relevant equations
    None I know of

    3. The attempt at a solution
    Previous calculations found that the hydrocarbon had a mass of 5.811g.

    Per empirical formula unit: (I determined the empirical formula to be CH, which was correct)

    molar mass of CH = 13.018g/mol

    5.811g / 13.018g/mol = 0.447 mol CH

    280kJ/0.447 mol = 627.266 kJ/mol

    My final answer was 627.266 kJ/mol but that was not correct.

    Am I interpreting the meaning of "empirical-formula unit" correctly?

    Any help is greatly appreciated.
  2. jcsd
  3. Oct 16, 2014 #2


    User Avatar

    Staff: Mentor

    Looks OK to me, perhaps it is just a matter of significant figures, or some rounding error?
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