chem question

[BodybldgDoc]

hey guys, can someone help me figure this one out.

What is delta Hf of H2O(g)?
A. -330KJ/mole
B. -286KJ/mole
C. -242KJ/mole
D. +242KJ/mole
E. +330KJ/mole

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[DentalKitty]

I'm pretty sure it's B. You have to combine the two equations and flip one to get the correct equation for the formation of water, but I don't have the numbers in front of me right now....or maybe that's the answer for the formation of liquid water, I can't remember

 

[Lonely Sol]

hey guys, can someone help me figure this one out.

What is delta Hf of H2O(g)?
A. -330KJ/mole
B. -286KJ/mole
C. -242KJ/mole
D. +242KJ/mole
E. +330KJ/mole

Well, you know:
H2(g) + 1/2O2(g) ---->h2O(l) -286kj/mole
h2O(g) ----->h2O(l) -44kj/mole

you are tryin to get H2(g) + 1/2O2(g) ---->h2O(g)

so the easiest way is to flip h2O(g) ----->h2O(l), now H = +44kj/mole

So, -286 + 44 = -242kj/mole Answer = C

 

[BodybldgDoc]

coolio thanks lonely