Question

What is meant by entropy driven reaction? How can the reaction with positive change of enthalpy and entropy be made entropy driven?

Answer 1

The free energy change of a reaction is given by ΔG = ΔH – TΔS 

For a reaction to be spontaneous, ΔG should be –ve. 

If both ΔH and ΔS are positive ΔG can be –ve if TΔS>ΔH in magnitude. Thus, entropy factor should dominate over enthalpy factor. Such reactions are therefore, called entropy driven. This can happen in either of the following two ways: 

(i) ΔS should be so large that even if T is low, TΔS should be greater than ΔH 

(ii) If ΔS is small, T should be so large that TΔS>ΔH.