What is Gibbs free energy?

Answer 1

Gibbs free energy is the free or available energy from a reaction. It is denoted by (Delta)G

Answer 2

Lancenigo di Villorba (TV), Italy

HISTORICAL NOTES

J. W. Gibbs was an american physician. He accomplished his academic formation during the second half of XIX century.
He interested to correlation thermodynamics theoretical aspects to experimental remarks. Scientists at the time developed thermodynamics fundaments starting mainly from "Steam Power" apparatus.
As it is known, "First Principe of Thermodynamics" may be written in mathematical terms, as follows :

d[E] = d[Q] + d[W]

where E is "Inner Energy" belonging to discussed System, Q and W are respectively "Heat and Work" that are energy's exchanges in/out-warding around the System.
Gibbs applied a well-known statement of Clausius (german physician), that is :

d[Q] =< T * d[S]

where S is Entropy as Clausius defined. The differential relation is a "Disequation" since NOT-Reversible process determine the "<" signus instead the "=" one. Moreover, Gibbs considerated only processes involving mechanical works (e.g. gas's expansion or compression), thus he put

d[W] =< 0 - p * d[V]

where V is the volume occupied by the System ; as you know, some incompressible matters (e.g. when they are not the gas) maintain its capacity, hence is volume.
Gibbs could write the disequation

d[E] =< T * d[S] - p * d[V]

As E or Inner Energy, Entropy is a "State's Function" that is a physico-chemical function variyng its value only depending on the "equilibrium's state" of the System. Since Q and W are not "State's Functions", you understand that the Gibbs writing is a most valuable tool.
Scientist knew also "Enthalpy" (e.g. it is named as H), thus Gibbs overcame to its formulation :

d[H] =< T * d[S] + V * d[p]

Gibbs understood "Enthalpy" was influenced by Entropy, in effects many processes involve "Entropy's changes", the latters able to spend part of "Enthalpy's ones".

GIBBS INTRODUCED "FREE ENERGY" as "Free Enthalpy's Energy" or Enthalpy free to be spent by System's evolutions.
Gibbs wrote :

d [G] = d[H] - d[T * S]

obtaining d [G] =< V * d[p] - S * d[T]. One more time you find a disequation ("<" signus for not-reversible processes, "=" for reversible ones) instead the direct relation binding H, S to G IS AN EQUATION FOR ANY EQUILIBRIUM's STATES. Furthermore, the disequation permits you state that "...any iso-T and iso-P processes may happen when you retrieve d[G] =< 0, nihil for reversible processes...".

I hope this helps you.

Answer 3

gibbs energy is the maximum amount of useful work that we can get from any reaction other than the pressure volume work.gibbs energy is given as
^G=^H - T^S
in case of electrochemical cells it is given as
^G=nFE

Answer 4

is the ultimate reason that motivate things happen