The fundamental active entity in the universe, defined as the capacity for doing work. Two famous equations relate energy to mass as either E = mc2 (Einstein) or E = hβn (Planck). These equations show that energy cannot be completely divorced from mass, as the two are to some extent interconvertible. The law of conservation of energy, simply stated, is that the sum total of energy in the universe is constant; therefore, energy cannot be either created or destroyed, but only converted from one form to another. Radiant energy (light) comprises the electromagnetic spectrum; all wavelengths of light are composed of photons or packets of energy traveling at the speed of light. Theoretically, they have no mass except that associated with their speed. Protons, electrons, and neutrons are forms of highly condensed energy that possess determinable mass but move at lower speeds. Energy is directly related to chemical phenomena in the formation and decomposition of compounds, in the many important reactions that occur in electrochemistry, and in the release of energy in nuclear fission and fusion. Free energy is a thermodynamic function; in chemical reactions, it is a measure of the extent to which a substance can react. Kinetic energy (the energy of motion) is most clearly exhibited in gases, in which molecules have much greater freedom of motion than in liquids and solids.See Radiation; Matter; Thermodynamics; Free Energy.Note: “One of the most difficult challenges we face is to find ways to ensure that all peoples of the world share more equitably the vast human benefits that energy can bring. The foundation of worldwide energy policy must be based on energy conservation and the development of additional sources through a judicious application of science and technology.” (Glenn T. Seaborg, ACS meeting, April 1976).
