The reaction,       Cr | Class 12 Chemistry Chapter General Principles and Processes of Isolation of Elements, General Principles and Processes of Isolation of Elements NCERT Solutions

Question:

The reaction,

      Cr2O3  +  2Al    →    Al2O3  + 2Cr            (ΔGo = -421kJ)

is thermodynamically feasible as is apparent from the Gibbs energy value. Why does it not take place at room temperature?

Answer:

The change in Gibbs energy is related to the equilibrium constant, K as

ΔG = - RT in K

At room temperature, all reactants and products of the given reaction are in the solid state. As a result, equilibrium does not exist between the reactants and the products. Hence, the reaction does not take place at room temperature. However, at a higher temperature, chromium melts and the reaction takes place.

We also know that according to the equation,

ΔG = ΔH - TΔ

Increasing the temperature increases the value of TΔS, making the value of Δmore and more negative. Therefore, the reaction becomes more and more feasible as the temperature is increased.


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Welcome to the NCERT Solutions for Class 12 Chemistry - Chapter . This page offers a step-by-step solution to the specific question from Excercise 1 , Question 3: The reaction,       Cr2O3  +  2Al    →    Al2O3....