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

    Staff: Mentor

    You have to take into account the enthalpy of solution. The Wikipedia entry 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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