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How can Hess' law be applied to this?

How can Hess' law be applied to this?

How can Hess' law be applied to this?

(OP)
Hello,

I am in the ME field, but my son asked me if I could answer this chemistry question. Naturally, I was quite embarrassed when I couldn't figure it out. Here it is:

Calculate the value of delta H for the formation of 1.00mol HI(g) from the following data:

H_2(g) + Cl_2(g) -> 2HCl(g)            Delta H= -184.4 kJ
HCl(g) + H_2_0(l) -> HCl(aq)           Delta H= -75.07 kJ
HI(g) + H_2_O(l) -> HI(aq)             Delta H= -80.30 kJ
KOH(aq) + HCl(aq) -> KCl(aq)           Delta H= -57.43 kJ
KOH(aq) + HI(aq) -> KI(aq)             Delta H= -57.14 kJ
Cl_2(g) + 2KI(aq) -> 2KCl(aq) + I_2(s) Delta H= -219.1 kJ

I understand the terminology, but I can't figure out how to apply Hess' law to this.  With none of the reactions having HI(g) isolated to one side, I am clueless.  At one point, I began to argue, with myself, that the question was a typo and should have specified HI(aq).  I don't think that is the case, however.  

Nonetheless, I am not looking for the answer to the question, but I am looking for a way to apply Hess' law to this.  If anyone could set me in the right direction, or even make some rough representations of how to set this up, I would greatly appreciate it.  You see, I have to figure this out before he does!

Thanks,
Michael

RE: How can Hess' law be applied to this?


These are the general rules for manipulating the equations:

1. One may reverse an equation; the sign of ΔHo must also be reversed.
2. Whenever cancelling terms from both sides of an equation the substances must be in identical physical states.
3. When multiplying or dividing the coefficients by a common factor, ΔHo must be likewise changed.

RE: How can Hess' law be applied to this?


Whatever the result you get from playing around with the above equations, the net result would be (according to a book on General Chemistry):

½I(s) + ½H2(g) → HI(g)       ΔH = +25.9 kJ

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