Entropy of a system ________. 

Explanation:

For any reversible process,

\({\rm{d }}S = \frac{δ Q}{T} + δ S_{gen}\)

For any reversible process,

δSgen = 0

\(\Rightarrow {\rm{d }}S = \frac{δ Q}{T} \)

Where;

dS = Change in entropy; dQ = Heat transferred; T = Temperature

⇒ Depending upon the type of heat transfer (Whether heat addition or heat rejection process) in the process, the entropy of the reversible process may increase or decrease.

• if there is a heat addition in the reversible process ⇒ Entropy of the reversible process will increase.
• if there is a heat rejection in a reversible process ⇒ Entropy of the reversible process will decrease.

 Additional Information

For an Isolated System:

\(\because\ {\rm{d }}S \geq \frac{δ Q}{T} \)

 ⇒ dS ≥ 0

• For Isolated system, no heat transfer occurs so entropy of an isolated system never decreases.
• The equality sign holds good when the process undergone by the system is reversible, the inequality sign holds good if there is any irreversibility present in the process. This statement is usually called the principle of entropy increase.
• Irreversible or spontaneous processes can occur only in that direction for which the entropy of the universe or that of an isolated system, increases. These processes cannot occur in the direction of decreasing entropy.

For an isolated system,

• ΔS > 0, for irreversible processes
• ΔS = 0, for reversible processes
• ΔS < 0, the process is impossible