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Homework Help: A tricky question

  1. Oct 19, 2007 #1
    Calculate the enthalpy change of the following reaction between nitrogen gas and oxygen gas, given thermochemical equations (1),(2),and(3).
    (1) 2H2(g) + O2(g) ---> 2H2O(l) H=-572KJ
    (2) N2O5 (g) + H2O(l) --->2HNO3 (l) H=-77KJ
    (3)1/2 N2 (g) + 3/2 O2 (g) +1/2 H2 (g) ---> HNO3 (l) H=-174KJ
  2. jcsd
  3. Oct 20, 2007 #2
    write equation of the reaction of nitrogen with oxygen. what is the product?

    notice that nitrogen and oxygen are both elements in their standard conditions. the product will be N2O5 only, so the equation is the enthalpy change of formation of N2O5.

    you only have to rearrange the above 3 eqns to obtain the enthalpy of formation of N2O5.
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