= -RTln K
where is standard Gibbs energy change, K is equilibrium constant, R is universal gas constant and T is temperature in kelvin scale
CH4 (g) + 2O2 (g) → CO2 (g) + 2H2O (l)
We know, RT
Δng is negative as product water in combustion reaction is in liquid state.
This implies ΔHo will be more negative than ΔUo
Hence, ΔHo < ΔUo
ΔH= -393.5 +2(-285.8)-(-890.3)
= -74.8 kJ/mo