We need to rearrange the individual steps in order for the sum to give the desired equation: CH_4(g) + 2O_2(g) → CO_2(g) + 2H_2O(l)CH4(g)+2O2(g)→CO2(g)+2H2O(l)
For that we will do the following: Step 1:
Since CH_4CH4 is needed to be in the reactant side, we will flip the reaction and in this case, we reverse the sign of DeltaGΔG: CH_4(g)->2H_2(g) + C(s)" " " "-Delta G = 51 kJCH4(g)→2H2(g)+C(s)−ΔG=51kJ
Step 2: 2H_2(g) + O_2(g) → 2H_2O(l) " " " "Delta G = -474 kJ2H2(g)+O2(g)→2H2O(l)ΔG=−474kJ
This equation will be left the way it is.
Step 3: C(s) + O_2(g) → CO_2(g)" " " "Delta G = -394kJC(s)+O2(g)→CO2(g)ΔG=−394kJ
This equation will be left the way it is.
Now we sum these three steps: CH_4(g)->cancel(2H_2(g)) + cancel(C(s))" " " "-Delta G = 51 kJCH4(g)→2H2(g)+C(s)−ΔG=51kJ cancel(2H_2(g)) + O_2(g) → 2H_2O(l) " " " "Delta G = -474 kJ2H2(g)+O2(g)→2H2O(l)ΔG=−474kJ cancel(C(s)) + O_2(g) → CO_2(g)" " " "Delta G = -394kJC(s)+O2(g)→CO2(g)ΔG=−394kJ -------------------−−−−−−−−−−−−−−−−−−− CH_4(g) + 2O_2(g) → CO_2(g) + 2H_2O(l)" " " "Delta G = -817kJCH4(g)+2O2(g)→CO2(g)+2H2O(l)ΔG=−817kJ
Here is a video about Hess's Law:
**Thermochemistry | Hess's Law, Enthalpy and Heating/Cooling Curve. **
