Heat of Formation for Ammonium chloride

[twilliams34]

Homework Statement

The problem statement is to find the heat of formation of NH₄CL using the calculated variables and two more reactions.
If I calculated it correctly the H_F for ammonia plus hydrochloric acid to be -247.7kj/mol. I am not sure what else it is that I need to do.

Homework Equations

I am not sure how I am supposed to calculate delta H to begin with, I think that's where my problems are laying at the moment.

The Attempt at a Solution

 

[TeethWhitener]

Ok I think I figured out what you did. It looks like you just added the heats of formation and aqueous heats of solution for ammonia and hydrogen chloride to get that number. What you need to do is use Hess’s Law: find the heat of reaction between gaseous ammonia and hydrogen chloride and then add these to the heats of formation of the reagents. This should give the correct answer.