Question

How would you determine if a reaction is entropy driven or enthalpy driven?

Answer 1

Hint:The entropy of a system is the spontaneity of the particles present in the system and it can be calculated by taking the difference between the entropy of the product and the reactants.
While on the other hand the enthalpy of a system is the change in energy of the system which is caused because of the absorption or release of heat.

Complete step-by-step answer:The terms enthalpy and entropy are two very prominent and significant terms in the field of thermodynamics. Both the terms have partly relation with each other in any reaction involving the absorb or release of energy or heat. Now, we will be considering both the terms individually and define them.
The term enthalpy can be defined as the change taking place in the internal energy and the volume of the system under the conditions of constant pressure. It is the quantity which deals with the heat which is present in the system. Therefore, the value of this quantity changes with the change in the heat of the system. For instance, the value of enthalpy increases when heat is added to the system and the value decreases when heat is released or removed from the system.
Now, if we consider the term entropy, it is the measure of the disorder or disorientation of the energy possessed by a collection of a number of particles. The idea of entropy is basically derived from thermodynamics, which would explain the heat transfer mechanism in a system.
Entropy change of a system is given by
 \[\Delta {{S}^{\circ }}_{reaction}=\Sigma {{S}^{\circ }}_{\{products\}}-\Sigma {{S}^{\circ }}_{\{reactants\}}\]
Where $\Delta S$ is the change in entropy, and the difference between the entropy of products (\[\Sigma {{S}^{\circ }}_{\{products\}}\]) and reactants \[\Sigma {{S}^{\circ }}_{\{reactants\}}\] gives the entropy change of the reaction.
Now if we consider the enthalpy change of a reaction, it is given by \[\Delta {{G}^{\circ }}=\Delta {{H}^{\circ }}-T\Delta {{S}^{\circ }}\] where, \[\Delta {{G}^{\circ }}\] is gibbs free energy, \[\Delta {{H}^{\circ }}\] is the change in enthalpy and \[T\] is the temperature, \[\Delta {{S}^{\circ }}\] is the entropy of the reaction.
So, in order to determine if the reaction is entropy driven or enthalpy driven, we need some data about these values. Generally the term entropy is more dominant but, we cannot guess unless we have the value of entropy and enthalpy.

Note:The prediction of a reaction whether its entropy driven or enthalpy driven, can be done by using the specific values of entropy and enthalpy.
However, in a general way, entropy is observed to be the dominant quantity, but we cannot guess the precise answer without the values.