Question

Calculate the standard heat of formation of acetaldehyde , 2C(s) + 2 H2(g) +1/2 O2 (g) ---> CH3CHO(g) given the following information?
CH3CHO(g) + 5/2 O2 (g) --> 2H2O(l) + 2 CO2(g) DeltaH rxn =-1194 KJ

H2(g)+ 1/2 O2 (g) --> H2O (l) DeltaH rxn =-286 KJ/mol

C(s) + O2(g) ---> CO2(g) DeltaH rxn=-394 KJ/mol


Ive tried flipping first equation then multiplying second equation and 3rd equation but I cannot get the correct answer which is -170 Kj . plus I can't get oxygen to 1/2 . PLEASE HELP ME AND SHOW ME WORK! THANKS !!
Reverse equation 1 and add to twice eqn 2 and twice equn 3. I didn't add dH to see that it comes out to -170 kJ but the equation you want is right so I assume the numbers will work.

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