![]() If the temperature is raised, then T ∆ S becomes more negative. In this reaction, the entropy (or) randomness decreases from left to right due to the consumption of gases. (i) The graphs for most metal to metal oxide reactions show a positive slope. An Ellingham diagram for oxides has several important features. These plots are useful to determine the relative ease of reducing a given metal oxide to the metal and also to predict the feasibility of the thermal reduction of an ore.Īn Ellingham diagram normally consists of plots of change in the Gibbs energy with temperature for the formation of oxides. This graphical representation is called an Ellingham diagram. The change in the Gibbs energy when 1gram molecule of oxygen, sulphur (or) halogen is used to form oxides, sulphides (or) halides of metals plotted against temperature. ∆ S = change in entropy during the reaction. ∆ G for any process at a given temperature is given by the equation The Gibbs energy is the most important thermodynamic term in metal extraction.įor a spontaneous reaction the change in the Gibbs energy, ∆ G, must be negative. It does not explained about the rate of the reaction.Thermodynamics useful to understand the variation in temperature required for the thermal reduction of oxides and to predict which element will suit as the reducing agent for a given metal oxide. The reactants and products are in equilibrium, which is not often true. Ex: Al reduces FeO, CrO and NiO in termite reaction but Al will not reduce MgO at a temperature below 1500 0C. Above this temperature, the free energy of formation of the oxide is positive the oxide becomes unstable and will decompose into the metal and dioxygen.Īny metal will reduce an oxide of another metal that lies above it in an Ellingham diagram. (iii) When the temperature is raised, a point will be reached where the graph crosses the line " ∆ G is zero." Below this temperature, the free energy of formation of the oxide is negative, so the oxide is stable. The temperature at which such a change occurs is indicated by an increase in the slope on the positive side. (ii) The Gibbs energy changes follow a straight line, unless the materials melt (or) vaporise. Thermodynamics useful to understand the variation in temperature required for the thermal reduction of oxides and to predict which element will suit as the reducing agent for a given metal oxide.
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