The Second Law of Thermodynamics states that the total entropy of an isolated system (which does not exchange matter or energy with surroundings) can never decrease over time.

• For a spontaneous process in an isolated system, the change in entropy is always positive: $\Delta S_{sys}>0$.
• The system will evolve towards a state of maximum entropy, which corresponds to thermodynamic equilibrium.
• $\Delta S_{universe}=\Delta S_{sys}+\Delta S_{surr}\ge 0$.