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Find the enthalpy for H3O

  1. Dec 7, 2005 #1
    I need to find the enthalpy for H3O. I can't find it in my table in my book, and I'm not having much luck finding it online. Is there one for this molecule? :confused:
     
  2. jcsd
  3. Dec 7, 2005 #2

    siddharth

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    What do you mean by enthalpy? Do you mean the standard enthalpy of formation?

    Remember that we can only measure the change in enthalpy of a system.
     
  4. Dec 7, 2005 #3
    I do mean the standard enthalpy of formation..
    The reaction is NH4+ in water to form NH3 + H3O+

    I can find NH4 and NH3, but not H3O
     
  5. Dec 7, 2005 #4

    Bystander

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    This is a "trick" question: the "trick" being that your text source has to inform you that ΔHf(H3O+) is "Zero" by convention, your instructor has to point this out, and you have to notice the special case.
     
  6. Dec 7, 2005 #5
    I'm really confused then. I'm supposed to show how there is a positive ΔH and a negative ΔH for the dissolution of ammonium nitrate. I did:

    NH4NO3 --> NH4+ + NO3-
    This is a ΔH of 28.1 kJ

    I thought maybe the negative ΔH was the Qh2o of the surrounding, but he said no, that the water does participate in the reaction. So I tried protonation..

    NH4+ + H2O --> NH3 + H3O+
    The ΔH is 372.2

    I'm not understanding how to show a negative ΔH here...
     
  7. Dec 7, 2005 #6

    Bystander

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    This statement makes absolutely NO sense: please give us an exact copy of the problem statement.
     
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