• Entropy of a system is a measure of the randomness of the system.
• Entropy is a function of state and it depends only on the initial and final state of the system and is independent of the path of the change.
• Entropy is also a factor affecting both chemical and physical changes.
• Spontaneous changes in an isolated system takes place with an increase in entropy.
• As the entropy related to a certain system is a function of state, the change in entropy can be calculated by subtracting the initial value of entropy from the final value of entropy.
∆S = S final – S initial
• For a chemical reaction, ∆S = S products – S reactants
• If this change is measured under the standard conditions ∆S θ = Sθ products – Sθ reactants
• The total influence of ∆Η and ∆S on a change is given by the Gibbs energy change which is ∆G. The relationship among these at constant temperature (T) is as follows.
∆G = ∆H – T∆S
At a constant temperature and pressure; for a spontaneous reaction ∆G < 0 for a reaction which is not spontaneous ∆G > 0 for a reaction at equilibrium ∆G = 0
Spontaneity of a system with a constant entropy (∆S = 0) is decided by ∆H and the spontaneity of a change that takes place under a constant enthalpy (∆H = 0) is decided by ∆S.
