Entropy is directly connected to the second law of thermodynamics, which states that:
In any spontaneous process, the total entropy of the universe always increases.
Key points:
- Universe = system + surroundings:
- Even if the entropy of a system decreases, the entropy of the surroundings usually increases by a greater amount, so the overall entropy increases.
- Direction of natural processes:
- Processes that increase the total entropy are spontaneous.
- Processes that decrease total entropy are non-spontaneous.
- Energy dispersal:
- The second law reflects that energy tends to spread out or disperse.
- Entropy measures how spread out energy and particles are in a system.
- Real-world examples:
- Ice melting: The water molecules become more disordered → entropy increases.
- Burning fuel: Energy is released as heat and gas spreads → entropy of surroundings increases.
In simple terms:
- Entropy is a measure of disorder, and the second law says that in any natural process, the universe moves toward more disorder or greater energy dispersal.