Gibbs Free Energy
They therefore describe The relationship between the G) and the standard- state free energy of reaction (delta behind a chemical reaction is. The Relationship Between Enthalpy (H), Free Energy (G) and Entropy (S). Free Energy: . We will see how to relate the free energy change to the extent of a chemical reaction. Standards are defined precisely. Okay, so let. posavski-obzor.info this contains a pretty rigorous treatment of gibbs-helmholtz equation. – Satwik Pasani Nov 6 '13 at.
Standard-State Free Energies of Reaction Go for a reaction can be calculated from tabulated standard-state free energy data. Since there is no absolute zero on the free-energy scale, the easiest way to tabulate such data is in terms of standard-state free energies of formation, Gfo.Free energy and cell potential - Redox reactions and electrochemistry - Chemistry - Khan Academy
As might be expected, the standard-state free energy of formation of a substance is the difference between the free energy of the substance and the free energies of its elements in their thermodynamically most stable states at 1 atm, all measurements being made under standard-state conditions.
We are now ready to ask the obvious question: What does the value of Go tell us about the following reaction? Go therefore describes this reaction only when all three components are present at 1 atm pressure.
The sign of Go tells us the direction in which the reaction has to shift to come to equilibrium.
The fact that Go is negative for this reaction at 25oC means that a system under standard-state conditions at this temperature would have to shift to the right, converting some of the reactants into products, before it can reach equilibrium. The magnitude of Go for a reaction tells us how far the standard state is from equilibrium. The larger the value of Go, the further the reaction has to go to get to from the standard-state conditions to equilibrium.
Assume, for example, that we start with the following reaction under standard-state conditions, as shown in the figure below. If we could find some way to harness the tendency of this reaction to come to equilibrium, we could get the reaction to do work.
Free energy and equilibrium
The free energy of a reaction at any moment in time is therefore said to be a measure of the energy available to do work. When a reaction leaves the standard state because of a change in the ratio of the concentrations of the products to the reactants, we have to describe the system in terms of non-standard-state free energies of reaction.
The difference between Go and G for a reaction is important.
There is only one value of Go for a reaction at a given temperature, but there are an infinite number of possible values of G. When a ball rolls down a hill, it is moving from a higher gravitational potential higher internal energy thus higher potential for work to a lower gravitational potential lower internal energy. In the same way, as molecules move, react, dissolve, melt, etc. A simple example is a system of dilute molecules diffusing in a homogeneous environment.
In this system, the molecules tend to move from areas with high concentration to low concentration, until eventually the concentration is the same everywhere. The microscopic explanation for this is based in kinetic theory and the random motion of molecules. However, it is simpler to describe the process in terms of chemical potentials: For a given temperature, a molecule has a higher chemical potential in a higher-concentration area, and a lower chemical potential in a low concentration area.
Movement of molecules from higher chemical potential to lower chemical potential is accompanied by a release of free energy. Therefore, it is a spontaneous process. Another example, not based on concentration but on phase, is a glass of liquid water with ice cubes in it.