Question #b62d7

1 Answer
Dec 2, 2015

Answer:

#Delta G = -817kJ#

Explanation:

To solve this question we will use Hess's Law:

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)#

For that we will do the following:
Step 1:
Since #CH_4# is needed to be in the reactant side, we will flip the reaction and in this case, we reverse the sign of #DeltaG#:
#CH_4(g)->2H_2(g) + C(s)" " " "-Delta G = 51 kJ#

Step 2:
#2H_2(g) + O_2(g) → 2H_2O(l) " " " "Delta G = -474 kJ#
This equation will be left the way it is.

Step 3:
#C(s) + O_2(g) → CO_2(g)" " " "Delta G = -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 kJ#
#cancel(2H_2(g)) + O_2(g) → 2H_2O(l) " " " "Delta G = -474 kJ#
#cancel(C(s)) + O_2(g) → CO_2(g)" " " "Delta G = -394kJ#
#-------------------#
#CH_4(g) + 2O_2(g) → CO_2(g) + 2H_2O(l)" " " "Delta G = -817kJ#

Here is a video about Hess's Law:
Thermochemistry | Hess's Law, Enthalpy and Heating/Cooling Curve.