Energy Definition in Chemistry and Physics

Definition of Energy in Science

Swirls of light and heat
Heat and light are two forms of energy. Mmdi/Getty Images

Energy Definition

Energy is defined in science as the ability to do work. It is a scalar physical quantity. Although energy is conserved, there are many different types of energy, such as kinetic energy, potential energy, light, sound, and nuclear energy. One form of energy may be converted into another without violating a law of thermodynamics.

When energy is "lost", it means the energy can't be recaptured for use.

This usually occurs when heat is produced.

The term "energy" comes from the Greek word energeia or from the French words en meaning in and ergon which means work.

Energy may be either renewable or nonrenewable. Photosynthesis is an example of a process the produces renewable energy. Burning coal is an example of nonrenewable energy. The plant continues to produce chemical energy in the form of sugar, by converting solar energy. Once coal is burned, the ash can't be used to continue the reaction.

The usual unit of energy is the joule (J).

Forms of Energy

There are many different forms energy can take. Here are some examples:

  • kinetic energy - energy of motion
  • potential energy - energy at rest, based on position in space
  • nuclear energy - energy released by changes in the atomic nucleus, such as fission or fusion
  • electrical energy - energy based on the attraction, repulsion, and movement of electrical charge, such as electrons, protons, or ions
  • chemical energy - energy based on the difference between the amount required to form chemical bonds versus how much is needed to break them