The First Law of Thermodynamics

The first law of thermodynamics is one of the fundamental governing laws of the physical universe, and comprises three separate but related concepts:

  • Energy is conserved.
  • Energy has many forms.
  • Energy can be converted from one form to another.

Conservation of energy grounds all processes in the natural world. A system can never produce more energy than it consumes.

Open v Closed Systems

For the Laws of Thermodynamics, a closed system exchanges neither energy nor matter with surrounding systems. In the observable world, every system is open because it is connected with another system or its surrounding environment. For example, even Earth, which is separated from the rest of the solar system by the atmosphere, receives radiant energy from the sun.

The total amount of energy in a closed system remains constant. It can only be changed from one form to another or transferred from one body to another. Another way to consider this concept is that the best outcome in a closed system is to break even; there will never be more energy at the end than at the beginning.

The second implication of the law states that energy exists in different forms. The different forms of energy manifest in nature, such as the chemical energy stored in the bonds of molecules of fuels such as petroleum, coal, wood, or natural gas. Sometimes energy exists in a more tangible form such as directed radiant energy—a laser beam or lighting from incandescent bulbs—or the mechanical energy of a moving object. The typical forms of energy include chemical (c), atomic (a), electrical (e), mechanical (m), radiant (r), and thermal (t).

The third implication of the first law provides the most use because energy can be converted between its different forms. For example, forms convenient for storage, such as the chemical energy in a cord of firewood become useful thermal energy emanating from a fireplace that warms a house. Intentional and thoughtful transformation of energy from one form to another enables many aspects of developed society: physical mobility, climate control, and refrigeration. And, as noted in an earlier section, this intentional transformation distinguishes humans from other species.

Image Credits: Oleksiy Mark/

Your browser is out-of-date!

Update your browser to view this website correctly.Update my browser now