Heat of Formation problem

[andyjl]

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C(s) + O2(g) --> CO2(g) delta H = -94 kcal/mol
H2(g) + 1/2 O2 -- > H2O(l) delta H = -68.3 kcal/mol
CO2(g) + 2H2O(l) --> 2O2(g) + CH4 delta H = 212 kcal/mol

The problem asks what is the heat of formation of methane.

so the only thing to do here is to multiply by 2 to the second reaction, but I initially thought that by multiplying two it does not change the ratios of the molar coefficients of the second reaction, so therefore it wouldn't change the delta H either. But the answer says you need to multiply the delta H by 2, why is that?

 

[Jasoos]

the ratio is not cahnged, but if the amounts are changed, then
( like 2 H2 + o2 - - > 2H2O ) then Delta H needs to be doubled cause the amount of heat produced by 2 moles of rxns is double the amt of heat produced by one mole, ant the overall reaction features two moles of said rxn

 

[andyjl]

thyanks