Any chemistry buffs here?

[Nate]

Okay, I can't find anything on the net that explains it simply...

I'm in second semester chemistry, because my nuke school credits allowed me to skip first semester...but, there are some things we didn't cover in nuke school, and I don't know how to do it...

Long story short, I can't figure out how to...well, I'll give you the problem...keep in mind I can't do subscripts.

Consider the process by which lead chloride dissolves in water:

PbCl2(s) -------> Pb^2+(aq) + 2Cl^-(aq)

Using data from tables in Chapter 8, calculate ΔH for this reaction.

This is the data I believe is applicable, the table is entitled "Standard Enthalpies of Formation at 25 degrees C (kJ/mol) of compounds at 1 atm, Aqueous Ions at 1 M":

PbCl2(s) is -359.4
Pb^2+ (aq) is -1.7
Cl^-(aq) is -167.2

What do I do? ^^;;

Help is greatly appreciated.

[Ingemar]

Have you ever heard of Hess's Law? It states that no matter what "path" you take to do a certain reaction, the enthalpy of reaction will always be the same. Normally, when they give you thermochemistry questions like this, they will give you several chemical equations (with enthalpies of reaction) and you must combine them in a way such that you will end up with the "desired" chemical equation.

That doesn't look like the case in this problem. You are given standard molar enthalpies of formation. Since lead chloride is being devolved rather than formed in this equation (it is on the left rather than the right), you have to change the sign of the delta H. Also, since you have two moles of chloride in the reaction, you have to multiply its delta H by two. All you have to do from there is combine the enthalpies of formation and that should get you the reaction enthalpy.

I -do- think this problem may involve Hess's law. If there are chemical equations associated with the standard enthalpies of formation given, it would help a lot if you showed them.