chemistry
posted by anna .
Hi,
I can't figure out how to start this one. I know I need to figure out the proportions or something of that sort. Any help is greatly appreciated Thanks!
Calculate ƒ¢H for the reaction
NO(g) + O(g) ¨ NO2(g)
given the following:
NO(g) + O3(g) ¨ NO2(g) + O2(g)
ƒ¢H = 198.9 kJ
O3(g) ¨ 3/2 O2(g)
ƒ¢H = 142.3 kJ
O2(g) ¨ 2O(g)
ƒ¢H = 495.0 kJ

I assume those strange symbols stand for delta H.
Write equation 1 as is.
Reverse equation 2 and add to 1.
Take 1/2 of equation 3 and reverse it; add to the other two.
When you reverse an equation you change the sign of delta H. If you take 1/2 of an equation you take 1/2 delta H.