Question

The reaction, Cr2O3 + 2Al → Al2O3 + 2Cr (△G0 = -421 kJ) is thermodynamically feasible as is apparent from the Gibbs energy value. Why does it not take place at room temperature?

Answer 1

Answer:

monoclinic

Explanation:

because rombic reactions takes place in room temperature at 95.6 degree Celsius but monoclinic reactions takes place at above the room temperature.

Answer 2

• The Gibbs energy value for the given reaction Cr2O3 + 2Al → Al2O3 + 2Cr is negative.
• This means that the process is thermodynamically feasible.
• However, the given reaction does not take place at room temperature. This can be explained using the relation : ΔG = ΔH - TΔS

where, ΔG = change in Gibbs free energy

            ΔH = change in enthalpy

               T = temperature of the system

             ΔS = change in entropy

• ΔH for the above reaction is positive. Therefore, for the process to be feasible, ΔG should be negative which is only possible when the magnitude of TΔS is greater than ΔH.
• At room temperature the magnitude of TΔS < ΔH.
• Hence, for the reaction to take place, temperature should be high.