2480.6 kJ required.
For:
CH_(4(g))+2O_(2(g))rarrCO_(2(g))+2H_2O_((l))CH4(g)+2O2(g)→CO2(g)+2H2O(l)
DeltaH_(comb)=-882.0"kJ"
So for the reverse reaction:
CO_(2(g))+2H_2O_((l))rarrCH_(4(g))+2O_(2(g))
DeltaH=+882.0"kJ"
[M_r]CH_4=16.0
So 16.0"g" requires 882.0"kJ"
So 1"g"rarr882.0/16.0"kJ"
So 45"g"rarr(882.0)/(16.0)xx45=2480.0"kJ"