The Second Law of Thermodynamics

The second law of thermodynamics states that energy spontaneously tends to flow only from being concentrated in one place to becoming diffused or dispersed and spread out. It is also called the law of entropy. Entropy measures the spontaneous dispersal of energy: how much energy is spread out in a process, or how widely spread out it becomes — at a specific temperature.

While quantity of matter or energy remains the same (First Law), the quality of matter/energy deteriorates gradually over time. Usable energy is inevitably used for productivity, growth and repair. In the process, usable energy is converted into unusable energy. Thus, usable energy is irretrievably lost in the form of unusable energy. 

Examples of the second law include:

• the increase in the volume of a gas
• the spontaneous mixing of different gases and liquids
• heating a substance
• the addition of a small amount of solute into a solvent
• spontaneous exothermic reactions