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Homework Help: Calculate heat released in the reaction

  1. May 3, 2014 #1


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    1. The problem statement, all variables and given/known data
    All the substances involved in the reaction given below can undergo combustion reaction and their combustion enthalpies at 300K are given below,
    2A(g)+B(g) ----> 3C(g) + D(g)
    Given: ΔH A = -1000cal/mol ΔH B= -2000cal/mol ΔH C=-500 cal/mol ΔH D = -100 cal/mol
    If the reaction occurs at constant volume at 300K and the reaction obeys first order with respect to A and if A reduces to half its initial amount in 69.3 sec, then calculate

    1) heat released when 2*10-3 mole of A has reacted at 300K(in cal)

    2) rate at which heat is released initially, if initially 1mol of A is present.

    3. The attempt at a solution

    ΔH of rxn = 2400 cal/mol
    ΔH = ΔU + Δng RT
    Since the reaction occurs at constant volume ΔQ = ΔU
    ΔQ = ΔH - Δng RT

    Substituting appropriate values , I get ΔQ = 1800 cal/mol. But this is not the correct answer.
  2. jcsd
  3. May 4, 2014 #2
    Where does it ask for ΔQ PER MOLE??
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