The law of conservation energy, first discovered by James Prescott Joule (1818-1889) in 1851, which holds that energy can neither be created nor destroyed, but that it can change form. It applies to closed systems in which the total amount of energy of all kinds is constant. While all natural processes conform to this law, not all processes doing so occur in nature. In fact, most natural processes occur in open systems and are thus irreversible (i.e., they proceed in one direction). This gave rise to the second law of thermodynamics and to irreversible thermodynamics.
See Classical thermodynamics, Closed system, Irreversible thermodynamics, Joule, Open system, Second law of thermodynamics