# chemistry

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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

• chemistry -

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.

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