I am a bit confused about calculation of Gibbs free energy for the folowing equation:
CH4 = C + 2H2
I considered C as graphite, CH4 and H2 as gas.
According to my calculation, DH = 74, DS = 0.080844
So the reaction will be spontaneous at 915 k (642 C) according to DG = DH - T*DS (putting DG =0)
But I have found two papers where they indirectly mentioned that they found DH =90 for this equation which gives spontaneous reaction temperature at 1113 k (840 C).
Can anyone please explain??
Also, why do we consider C as graphite, not as gaseous? Is it because of temperature??