The enthalpy change for a reaction does not depend upon :

The correct relationship between free energy change in a reaction and the corresponding equilibrium constant K_c is :

If at 298 K the bond energies of C - H, C - C, C = C and H - H bonds are respectively 414, 347, 615 and 435 kJ/mol, the value of enthalpy change for the reaction
H₂C = CH₂(g) + H₂(g) $$\to$$ H₃C - CH₃(g) at 298 K will be :

For the reactions
2C + O₂ $$\to$$ 2CO₂; $$\Delta H$$ = -393 J
2Zn + O₂ $$\to$$ 2ZnO; $$\Delta H$$ = -412 J