Given C_("graphite") + O_(2)(g) to CO_(2)(g), Delta_(r)H^(@) = -393.5 kJ"mol"^(-1) H_(2)(g) + 1/2O_(2)(g) to H_(2)O(l), DeltaH^(@) = -285.8 kJ"mol"^(-1) CO_(2)(g)+ 2H_(2)O(l) to CH_(4)(g) + 2O_(2)(g), DeltaH^(@) = +890.3 kJ"mol"^(-1) Based on the above thermochemical equations, the value of Delta H^(@) at 298 K for the reaction C_("graphite") + 2H_(2)(g) to CH_(4)(g) will be :

Given C_("graphite") + O_(2)(g) to CO_(2)(g), Delta_(r)H^(@) = -393.5

1.	Given C_("graphite") + O_(2)(g) to CO_(2)(g), Delta_(r)H^(@) = -393.5 kJ"mol"^(-1) H_(2)(g) + 1/2O_(2)(g) to H_(2)O(l), DeltaH^(@) = -285.8 kJ"mol"^(-1) CO_(2)(g)+ 2H_(2)O(l) to CH_(4)(g) + 2O_(2)(g), DeltaH^(@) = +890.3 kJ"mol"^(-1) Based on the above thermochemical equations, the value of Delta H^(@) at 298 K for the reaction C_("graphite") + 2H_(2)(g) to CH_(4)(g) will be :
Answer» `+ 748 KJ` `+ 144.0 kJ` `-74.8 kJ` `-144.0 kJ` Solution :(i) `C("graphite") + O_(2) to CO_(2)(g) DeltaH^(@) = -393.5 kJ"mol"^(-1)` (ii) `H_(2)(g) + 1/2O_(2)(g) to H_(2)O(l)DeltaH ^(@) - 285.8 kJ"mol"^(-1)` (iii)`CO_(2)(g) + 2H_(2)O(l) to CH_(4)(g) + 2O_(2)(g)DeltaH = 890.3 kJ"mol"^(-1)` The required equation is (IV)` C_("graphite") + 2H_(2)(g) to CH_(4)(g)DeltaH ^(@) = `? By applying eq.(i) + 2 xx eq.(ii) + eq.(iii) `DeltaH^(@) = -393.5 + 2(-285.8) + 890.3 = -74.8 kJ"mol"^(-1)`