Ellingham diagram (ΔG° vs T for metal oxide reduction) (ΔG° = ΔH° − TΔS°: free energy change determines spontaneity of reduction; lower line)
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ΔG° = ΔH° − TΔS° — free energy change determines spontaneity of reduction; lower line reduces upper oxide
What each symbol means
| Symbol | What it stands for |
|---|---|
| T | Absolute temperature (K) |
| ΔG° | Standard Gibbs free energy change (kJ/mol) |
| ΔH° | Standard enthalpy change (kJ/mol) |
| ΔS° | Standard entropy change (kJ/mol·K) |
When to use this
At temperature where reducing agent's ΔG° line lies BELOW metal oxide line, reduction is thermodynamically feasible. CO line slopes downward because 2CO has more entropy than C + O₂. Metal oxide lines generally slope upward.