question_answer

Reduction of \[C{{r}_{2}}{{O}_{3}}\]with Al is thermodynamically feasible; but it does not take place at room temperature. Assign reason.

Answer:

                In terms of thermodynamics, the thermit reduction may be written as: \[2/3C{{r}_{2}}{{O}_{3}}(s)+4/3\,Al(s)\xrightarrow{\,}\,4/3\,Cr(s)+2/3\]\[A{{l}_{2}}{{O}_{3}}(s);\,\,\Delta {{G}^{o}}\,=-287\,\,kJ\] The reduction is feasible as such. However, a careful look reveals that all the reactant and product species are solids. Therefore, the reaction does not take place at room temperature. Upon heating, chromium melts which means that \[\Delta S\]will tend to increase thereby making the reaction feasible.