Case – I : [Coke as reducing agent]
ZnO + C → Zn + CO,
∆G° becomes lesser as the T is more then 1120K.
Case – II : [CO as reducing agent]
ZnO + CO2 → Zn + CO, ∆G° becomes lesser when the T is more then 1323K.
→ The value of ∆G° is negative for a reaction to occur.
→ In the equation (1)
∆G° becomes negative at low temperature- so equation (1) is feasible i.r. C is a better reducing agent for ZnO.