Is Delta H of formation the same for NH4NO3 Aqueous and in Solid Form?

  1. I am doing a project in Chemistry and I need to use Hess' Law to cancel two equations and if in one equation the NH4NO3 is solid and in the second one the NH4NO3 is aqueous.

    The equations are:
    1: NH4NO3 (s) + HCl (aq) --> HNO3 (aq) + NH4Cl (aq)
    2: NH4OH (s) + HNO3 (aq) --> H2O (l) + NH4NO3 (aq)

    I will find the heat of reaction for both of these reactions and use those values and Hess' law to find the Delta H of this reaction:

    HCl (aq) + NH4OH (s) --> NH4Cl (aq) + H2O (l)


    I am wondering if these procedure will work because I created this myself for the project we are doing and I don't know:

    1. Whether these individual reactions work
    2. Whether they add up to the overall reaction and whether that reaction even works.

    The part that is getting me stuck up is whether I can use Hess' law to cancel and aqueous version of NH4NO3 with a solid version.

    Your knowledge and advice is much appreciated!
    Thank you!
     
  2. jcsd
  3. DrClaude

    DrClaude 2,285
    Science Advisor
    Homework Helper
    Gold Member

    You have to take into account the enthalpy of solution. The Wikipedia entry http://en.wikipedia.org/wiki/Enthalpy_change_of_solution lists a few values, including that for ammonium nitrate.

    [Edit: I don't know why I focussed on ammonium nitrate, which is not what you asked about. See Borek's much better answer.]
     
    Last edited: May 8, 2014
  4. Borek

    Staff: Mentor

    No such thing as solid NH4OH.
     
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