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Homework Help: Enthalpy of Formation

  1. Jan 23, 2010 #1
    1. The problem statement, all variables and given/known data

    Using the enthalpies of formation given below, calculate ΔH°rxn in kJ, for the following reaction.

    3NO2(g)+1H2O(l) -> 2HNO3(g)+1NO(g)

    NO2 (g): 33.10 kJ/mol
    H2O (l): -285.83 kJ/mol
    HNO3 (l): -174.10 kJ/mol
    NO (g): 90.29 kJ/mol

    2. Relevant equations

    dHrxn = dHproducts - dHreactants

    3. The attempt at a solution

    Is this possible to do since the equation says HNO3 is a gas, but they give the enthalpy of formation for HNO3 as a liquid.
  2. jcsd
  3. Jan 26, 2010 #2
    its possible but you need to use another enthalpy term that accounts for the latent heat which is from the phase transfer of liquid to gas
  4. Jan 27, 2010 #3


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    That would be the Hvap of HNO3.
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