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04 May 15
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Gibbs free energy
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maximum amount of non-expansion work that can be extracted from a thermodynamically closed system (one that can exchange heat and work with its surroundings, but not matter); this maximum can be attained only in a completely reversible process
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When a system changes from a well-defined initial state to a well-defined final state, the Gibbs free energy change ΔG equals the work exchanged by the system with its surroundings, minus the work of the pressure forces, during a reversible transformation of the system from the initial state to the final state
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there is a general natural tendency to achieve a minimum of the free energy
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When the calculated energetics of the process indicate that ΔG is negative,
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reaction will be favoured
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will release energy
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if conditions indicated a positive ΔG
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then energy—in the form of work—would have to be added to the reacting system for the reaction to occur
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09 Oct 14
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When a system changes from a well-defined initial state to a well-defined final state, the Gibbs free energy ΔG equals the work exchanged by the system with its surroundings, minus the work of the pressure forces, during a reversible transformation of the system from the same initial state to the same final state.
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20 Feb 14
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Gibbs energy (also referred to as ∆G) is also the chemical potential that is minimized when a system reaches equilibrium at constant pressure and temperature
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greatest amount of mechanical work which can be obtained from a given quantity of a certain substance in a given initial state, wit
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the German scientist Hermann von Helmholtz stated that affinity is the largest quantity of work which can be gained when the reaction is carried out
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Until this point, the general view had been such that: “all chemical reactions drive the system to a state of equilibrium
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- U is the internal energy (SI unit: joule)
- p is pressure (SI unit: pascal)
- V is volume (SI unit: m3)
- T is the temperature (SI unit: kelvin)
- S is the entropy (SI unit: joule per kelvin)
- H is the enthalpy (SI unit: joule)
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nd if ΔStot = 0 then the process is reversibl
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becomes:
favoured reaction (Spontaneous)
Neither the forward nor the reverse reaction prevails (Equilibrium)
disfavoured reaction (Nonspontaneous)
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thermodynamic processes are not confined to the two dimensional P-V diagram. T
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energy inputs from other energy sources (including the sun and exothermic chemical reactions) are "coupled" with reactions that are not entropically favored (have a Gibbs free energy less than zero).
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17 Dec 13
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01 Oct 13
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The Gibbs free energy is the maximum amount of non-expansion work that can be extracted from a closed system; this maximum can be attained only in a completely reversible process.
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such as at the close of the processes are left in their initial condition.[3]
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21 Oct 12
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thermodynamic potential that measures the "useful" or process-initiating work obtainable from a thermodynamic system at a constant temperature and pressure
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The Gibbs free energy is the maximum amount of non-expansion work that can be extracted from a closed system; this maximum can be attained only in a completely reversible process
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In essence, this means that such a reaction will be favoured and will release energy
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The energy released equals the maximum amount of work that can be performed as a result of the chemical reaction. In contrast, if conditions indicated a positive ΔG, then energy—in the form of work—would have to be added to the reacting system to make the reaction go.
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06 Dec 11
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measures the "useful" or process-initiating work obtainable from a thermodynamic system at a constant temperature and pressure (isothermal, isobaric)
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the maximum amount of non-expansion work that can be extracted from a closed system
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The quantity called "free energy" is a more advanced and accurate replacement for the outdated term affinity, which was used by chemists in previous years to describe the force that caused chemical reactions.
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According to chemistry historian Henry Leicester, the influential 1923 textbook Thermodynamics and the Free Energy of Chemical Substances by Gilbert N. Lewis and Merle Randall led to the replacement of the term "affinity" by the term "free energy" in much of the English-speaking world.
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08 Oct 11
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Gibbs free energy
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a thermodynamic potential that measures the "useful" or process-initiating work obtainable from a thermodynamic system at a constant temperature and pressure (isothermal, isobaric).
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14 Mar 07
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- Main article: Entropy and life
To a good approximation, one of the most oft-quoted references in thermodynamics is Erwin Schrödinger’s 1944 postulate that an organism keeps itself alive or aloof by feeding on negative entropy from its environment.[8] From the famous chapter six “Order, Disorder and Entropy” of his book What is Life?, Schrödinger asks: “what is the characteristic feature of life? and “when is a piece of matter said to be alive?” To answer these questions, Schrödinger turns to thermodynamics. Life, according to Schrödinger, avoids a decay to maximum entropy, or thermodynamic equilibrium, which Schrödinger equates with death, by feeding on negative entropy. Specifically, according to Schrödinger, an organism avoids decay by eating, drinking, breathing, and in the case of plants assimilating, a process called metabolism.
In the past, Schrödinger states, this process would have been considered an exchange of matter or energy, such that organisms stay alive by exchanging energy. He uses the example of how caloric values are printed in certain menus in the United States or Germany, but states that these caloric energy exchange values are useless in trying to quantify life. He then asks “what then is that precious something contained in our food which keeps us from death?” The answer, according to Schrödinger, is that because according the second law of thermodynamics an organism continually produces “positive entropy” it must continually draw in “negative entropy” from its environment to stay alive. Or, specifically “the essential thing in metabolism is that the organism succeeds in freeing itself from all the entropy it cannot help producing while alive.”
These suppositions, because they were intended for a lay audience, however, met with great opposition in the physics community. In later editions of his book, Schrödinger attached a note to chapter six explaining his use of the term “negative entropy”. He states “the remarks on negative entropy have met with doubt and opposition from physicist colleagues. Let me say first, that if I had been catering for them alone I should have let the discussion turn on free energy instead. It is the more familiar notion in this context. But this highly technical term seemed too linguistically near to energy for making the average reader alive to the contrast between the two things.”
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favoured reaction (Spontaneous)
Neither the forward nor the reverse reaction prevails (
disfavoured reaction (Nonspontaneous)
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