For spontaneous changes in an isolated system (S = entropy)
A. Ds = 0
B. Ds <0
C. Ds > 0
D. Ds = Constant
Answer: Option C.
Explanation:
By second law of thermodynamics the TdS≥δQ
For an isolated system δQ=0
⇒ for an irreversible (nothing but spontaneous process) dS>0 and for an reversible (or the system at equilibrium) dS=0