Hey again.

Ill just copy the question here, but basically I need someone to explain how this equation is solved using (products minus reactants) for formation enthalpies.

Calculate the average C - H bond energy for methane

DeltaHformation(kj/mol) CH4 = -75

DeltaHformation(kj/mol) C(gas) = 717

DeltaHformation(kj/mol) H(gas) = 218

this is where i keep getting stuck...

C(s) + 2H2(g) = CH4(g)

717 + 4(218) = X Delta H= -75

When i find out X, by going X-(717+4(218))=-75, then divide by four, the answer is wrong... I was wondering if someone could do this problem and show me how you did it...

Also, i cant really understand how you can use the enthalpy of formation, then divide by 4, to find the bond energy?

!?! I know there are 4 c-h in it, but just the fact that enthalpies of formation are used, seems strange...

Thanks.