Question

Use the thermochemical equations shown below to determine the enthalpy for the reaction:
C(s) + 2H2(g) → CH4(g)

CO2(g) → C(s) + O2(g) ΔH = 295.1 kJ
H2(g) + ½ O2(g) → H2O(l) ΔH = -214.3 kJ
CH4(g) + 2O2(g) → CO2(g) + 2H2O(l) ΔH = -667.9 kJ

Answer 1

We are going to be using Hess law which states:
"The standard enthalpy of an overall reaction is the sum of the standard enthalpies of the individual reactions into which a reaction may be divided."

In addition you may use that:
\[\Large \Delta H ^{\Theta}(A \to B)=-\Delta H ^{\Theta}(B \to A)\]

So what to do is:
1) Add the equations together to yield the wished equation
2) From the way the equations are added, use hess law to write up the expression for the wish reaction
3) Calculate the enthalpy for the wished reaction.