Energy

{{MitoPedia |abbr=various [J] |description=Energy [J] is a fundamental term that is used in physics and physical chemistry with various meanings. These meanings become explicit in the following equations relating to systems at constant temperature and pressure. Energy is exchanged between a system and the environment across the system boundaries in the form of [[heat], ∆_eQ and work, ∆_eW

 ∆H = ∆eQ + ∆eW [Eq. 1]

Whereas ∆H describes the energy change (enthalpy) of the system, heat and work are external changes (subscript e). The energy balance equation [Eq. 1] is a form of the First Law of Thermodynamics, which is the law of energy conservation stating that energy cannot be generated or destroyed: energy can only be transformed into different forms of work and heat.

An equally famous energy balance equation considers energy changes of the system only:

∆H = ∆G + T∙∆S = ∆G + ∆B [Eq. 2]

The total energy (enthalpy, ∆H) change of a system (at constant pressure and temperature) is the sum of free energy change (Gibbs energy, ∆G) and bound energy change (bound energy, ∆B = T∙∆S). The bound energy is that part of the total energy change that is always bound to an exchange of heat (at constant temperature). Therefore, if a process occurs at equilibrium, when ∆G = 0, then ∆H = ∆B, and with [Eq. 1] (at ∆_eW = 0) we obtain the definition of the bound energy as the heat change taking place in an equilibrium process,

∆B = T∙∆S = ∆eQeq [Eq. 3]

When talking about energy transformations, the term energy is used in a general sense without specification of these various forms of energy. |info=Coopersmith 2010 Oxford Univ Press }}

MitoPedia concepts: Ergodynamics