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单词 free energy
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free energy


free energy

n.1. A thermodynamic quantity that is the difference between the internal energy of a system and the product of its absolute temperature and entropy; the capacity of a system to do work, as in an exothermic chemical reaction.2. A thermodynamic quantity that is the difference between the enthalpy and the product of the absolute temperature and entropy of a system. Also called Gibbs free energy.

free energy

n (General Physics) a thermodynamic property that expresses the capacity of a system to perform work under certain conditions. See Gibbs function, Helmholtz function
Thesaurus
Noun1.free energy - (physics) a thermodynamic quantity equivalent to the capacity of a physical system to do workfree energy - (physics) a thermodynamic quantity equivalent to the capacity of a physical system to do work; the units of energy are joules or ergs; "energy can take a wide variety of forms"energynatural philosophy, physics - the science of matter and energy and their interactions; "his favorite subject was physics"physical phenomenon - a natural phenomenon involving the physical properties of matter and energyactivation energy, energy of activation - the energy that an atomic system must acquire before a process (such as an emission or reaction) can occur; "catalysts are said to reduce the energy of activation during the transition phase of a reaction"alternative energy - energy derived from sources that do not use up natural resources or harm the environmentatomic energy, nuclear energy - the energy released by a nuclear reactionbinding energy, separation energy - the energy required to separate particles from a molecule or atom or nucleus; equals the mass defectchemical energy - that part of the energy in a substance that can be released by a chemical reactionelectrical energy, electricity - energy made available by the flow of electric charge through a conductor; "they built a car that runs on electricity"energy level, energy state - a definite stable energy that a physical system can have; used especially of the state of electrons in atoms or molecules; "according to quantum theory only certain energy levels are possible"rest energy - the energy equivalent to the mass of a particle at rest in an inertial frame of reference; equal to the rest mass times the square of the speed of lightwork - (physics) a manifestation of energy; the transfer of energy from one physical system to another expressed as the product of a force and the distance through which it moves a body in the direction of that force; "work equals force times distance"heat, heat energy - a form of energy that is transferred by a difference in temperaturemechanical energy - energy in a mechanical formradiant energy - energy that is transmitted in the form of (electromagnetic) radiation; energy that exists in the absence of matterradiation - energy that is radiated or transmitted in the form of rays or waves or particles

free energy


free energy

or

Gibbs free energy,

quantity derived from the relationships between heat and work studied in thermodynamicsthermodynamics,
branch of science concerned with the nature of heat and its conversion to mechanical, electric, and chemical energy. Historically, it grew out of efforts to construct more efficient heat engines—devices for extracting useful work from expanding hot gases.
..... Click the link for more information.  and used as a measure of the relative stability of a physical or chemical system, i.e., the tendency of the system to react or change. If the change in free energy, ΔG, is negative, the transformation of the system will occur spontaneously, since transitions in which the energy decreases are favored, whereas those in which it increases (ΔG positive) are not. The change in free energy for a given process at a particular temperature depends on three factors, as seen from the equation ΔG = ΔH − TΔS, where ΔH is the change in the enthalpyenthalpy
, measure of the heat content of a chemical or physical system; it is a quantity derived from the heat and work relations studied in thermodynamics. As a system changes from one state to another the enthalpy change, ΔH,
..... Click the link for more information.  of the system, T is the temperature in degrees Kelvin, and ΔS is the change in entropyentropy
, quantity specifying the amount of disorder or randomness in a system bearing energy or information. Originally defined in thermodynamics in terms of heat and temperature, entropy indicates the degree to which a given quantity of thermal energy is available for doing
..... Click the link for more information. . A negative value of the enthalpy change indicates a decrease in the heat content of the system and contributes to a favorable value of the free energy; a positive entropy change indicates a decrease in the orderliness of the system and also contributes to a favorable value of the free energy, since a system tends to go from more ordered to less ordered states. It may happen that the change in enthalpy for the reaction is favorable but that of the entropy is unfavorable, or vice versa; in such a case the temperature is the deciding factor since it determines how much weight is given to the entropy change. For example, in the transition of liquid water to ice, the enthalpy change is favorable because heat is released in the process but the entropy change is unfavorable because the transition is to the more ordered, crystalline state. Below a temperature of 32&degF; (273&degK;) the enthalpy term, ΔH, is larger and the process is spontaneous, but at higher temperatures the entropy term, TΔS, predominates, and the transition does not occur. Although the free energy indicates whether or not a given reaction will occur, it gives no information about the speed of such a reaction. The reaction of hydrogen with oxygen to form water has a favorable, negative, free energy, but the reaction rate is so slow that without the presence of a catalyst it is not observable. Scientists use tables listing the standard free energy, ΔG°, of various compounds; the standard free energy is the change in free energy when one mole of the compound is formed at 25&degC; and 1 atmospheric pressure.

Free energy

A term in thermodynamics which in different treatments may designate either of two functions defined in terms of the internal energy E or enthalpy H, and the temperature-entropy product TS.

The function (E – TS) is the Helmholtz free energy and is the function ordinarily meant by free energy in European references. The Gibbs free energy is the function (H – TS). For the Lewis and Randall school of American chemical thermodynamics, this is the function meant by the free energy F. To avoid confusion with the symbol F as applied elsewhere to the Helmholtz free energy, the symbol G has also been used. Another development was the introduction of the name free enthalpy, with symbol G, for the Gibbs function. See Work function (thermodynamics)

For a closed system (no transfer of matter across its boundaries), the work which can be done (1)  in a reversible isothermal process is given by the series shown in Eq. (1). For these conditions, TΔS represents the heat given up to the surroundings. Should the process be exothermal, TΔS < 0, then actual work done on the surroundings is less than the decrease in the internal energy of the system. The quantity (ΔE - TΔS) can then be thought of as a change in free energy, that is, as that part of the internal energy change which can be converted into work under the specified conditions. This then is the origin of the name free energy. Such an interpretation of thermodynamic quantities can be misleading, however; for the case in which TΔS is positive, Eq. (1) shows that the decrease in “free” energy is greater than the decrease in internal energy.

For constant temperature and pressure in a reversible process the decrease in the Gibbs function G for the system again corresponds to a free-energy change in the above sense, since it is equal to the work which can be done by the closed system other than that associated with its change in volume ΔV under the given constant pressure P. The relations shown in Eq. (2) can be formed since ΔH = ΔE + PΔV. (2) 

Each of these free-energy functions is an extensive property of the state of the thermodynamic system. For a specified change in state, both ΔA and ΔG are independent of the path by which the change is accomplished. Only changes in these functions can be measured, not values for a single state.

The thermodynamic criteria for reversibility, irreversibility, and equilibrium for processes in closed systems at constant temperature and pressure are expressed naturally in terms of the function G. For any infinitesimal process at constant temperature and pressure, -dG ≥ δwnet. If δwnet is never negative, that is, if the surroundings do no net work on the system, then the change dG must be negative or zero. For a reversible differential process, -dG > δwnet; for an irreversible process, -dG > δwnet. The free energy G thus decreases to a minimum value characteristic of the equilibrium state at the given temperature and pressure. At equilibrium, dG = 0 for any differential process taking place, for example, an infinitesimal change in the degree of completion of a chemical reaction. A parallel role is played by the work function A for conditions of constant temperature and volume. Because temperature and pressure constitute more convenient working variables than temperature and volume, it is the Gibbs free energy which is the more commonly used in thermodynamics. See Entropy, Thermodynamic principles

Free Energy

 

a term used to refer to the Gibbs function and to the Helmholtz function, both of which are thermodynamic potentials. In Soviet usage, the term “free energy” is used primarily for the Helmholtz function.

The Helmholtz free energy, also called the work function, is defined as the difference between the internal energy U of a thermodynamic system and the product of the system’s entropy S and temperature T. The quantity ST, which is subtracted from the internal energy when the free energy is found, is sometimes called the bound energy.

free energy

[¦frē ′en·ər·jē] (thermodynamics) The internal energy of a system minus the product of its temperature and its entropy. Also known as Helmholtz free energy; Helmholtz function; Helmholtz potential; thermodynamic potential at constant volume; work function. Gibbs free energy

free energy


energy

 [en´er-je] power that may be translated into motion, overcoming resistance or causing a physical change; the ability to do work. Energy assumes several forms; it may be thermal (in the form of heat), electrical, mechanical, chemical, radiant, or kinetic. In doing work, the energy is changed from one form to one or more other form(s). In these changes some of the energy is “lost” in the sense that it cannot be recaptured and used again. Usually there is loss in the form of heat, which escapes or is dissipated unused; all energy changes give off a certain amount of heat.ƒ
All activities of the body require energy, and all needs are met by the consumption of food containing energy in chemical form. The human diet comprises three main sources of energy: carbohydrates, proteins, and fats. Of these three, carbohydrates most readily provide the kind of energy needed to activate muscles. Proteins work to build and restore body tissues. The body transforms chemical energy derived from food by the process of metabolism, an activity that takes place in the individual cell. Molecules of the food substances providing energy pass through the cell wall. Inside the cell, chemical reactions occur that produce the new forms of energy and yield by-products such as water and waste materials; see also adenosine triphosphate.free energy (Gibbs free energy (G)) the energy equal to the maximum amount of work that can be obtained from a process occurring under conditions of fixed temperature and pressure.nuclear energy energy that can be liberated by changes in the nucleus of an atom (as by fission of a heavy nucleus or by fusion of light nuclei into heavier ones with accompanying loss of mass).

free en·er·gy (F),

a thermodynamic function symbolized as F, or G (Gibbs free energy), = H - TS, where H is the enthalpy of a system, T the absolute temperature, and S the entropy; chemical reactions proceed spontaneously in the direction that involves a net decrease in the free energy of the system (that is, ΔG < 0).

free en·er·gy

(F) (frē en'ĕr-jē) A thermodynamic function symbolized as F, or G (Gibbs free energy), =H-TS, where H is the enthalpy of a system, T the absolute temperature, and S the entropy; chemical reactions proceed spontaneously in the direction that involves a net decrease in the free energy of the system (i.e., ΔG < 0).

free energy

the amount of energy that is available for work when released in a chemical reaction. For example, when a molecule of ATP is hydrolysed to ADP + P, the free energy released is about 34 kJ.
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free energy


Related to free energy: Gibbs free energy, perpetual motion, free electricity
  • noun

Synonyms for free energy

noun (physics) a thermodynamic quantity equivalent to the capacity of a physical system to do work

Synonyms

  • energy

Related Words

  • natural philosophy
  • physics
  • physical phenomenon
  • activation energy
  • energy of activation
  • alternative energy
  • atomic energy
  • nuclear energy
  • binding energy
  • separation energy
  • chemical energy
  • electrical energy
  • electricity
  • energy level
  • energy state
  • rest energy
  • work
  • heat
  • heat energy
  • mechanical energy
  • radiant energy
  • radiation
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更新时间：2024/12/23 22:20:55