Chemistry - Thermodynamics - II Question with Solution | TestHub
The graphical representation of Gibbs energy was first used by H.J.T. Ellingham. This provides a sound basis for considering the choice of reducing agent in the reduction of oxides. This is known as Ellingham Diagram. Such diagrams help us in predicting the feasibility of thermal reduction of an ore.
Which of the following is correct about the reaction ?
i) At , of the reaction is zero.
ii) Below , of the reaction is positive.
iii) Above , of the reaction is negative.
iv) Below , Mg can reduce , and the process is economical.
v) At , can reduce to .
vi) Below , Mg can reduce , and the process is not economical.
Options:
Answer:
Solution:
i) The temperature at which the Gibbs free energy change () for a reaction is zero is the point where the two relevant oxidation lines in the Ellingham diagram cross. For the reaction between Al₂O₃ and Mg, this point is .
v) Below , the line for the formation of MgO lies below the line for the formation of Al₂O₃, meaning Mg is a better reducing agent than Al at this temperature and can reduce Al₂O₃.
vi) While thermodynamically feasible below , the process is not considered economical, likely due to other practical or physical factors not detailed in the brief passage.