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

[member 508213]

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!

 

[DrClaude]

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.]

 

[Borek]

No such thing as solid NH₄OH.