[GGL/TH-08001] Gibbs Free Energy

1. Gibbs free energy, (as the name free energy suggest) is the maximum amount of non expansion work that can be obtained in a reversible manner for a closed system under the conditions of constant temperature and pressure.
2. These condition of reversibe, isothermal and isobaric process in the definition of Gibbs energy is because of its mathematical representation. G = H + TS
3. The concept was actually introduced to reduce the complexity of calculating entropy change in surrounding and to convert it in terms of system itself (second term in following equation's right hand side)
4. Del S (universe) = Del S (system) + Del S (surrounding)
5. In chemistry, the Gibbs energy [1] is useful because it relates properties of a system with the entropy change of the universe.
6. To predict whether a reaction is spontaneous, we need to know how it affects the entropy of the universe. We can do so by calculating ΔG=ΔH−TΔS=ΔU+PΔV−TΔ Note that this only makes reference to the pressure, volume, temperature, and entropy of the system, and not of the surroundings. If ΔG  is positive, then the entropy change for the universe is negative, and vice versa. This only holds when reactions are carried out at constant temperature and constant pressure, which is most often the case in chemistry. These constraints allow us to relate the entropy change of the universe to intensive and extensive quantities of the system. The Gibbs energy is much less useful under other conditions.
7. Gibbs energy is also a measure of the amount of work that can be extracted from a system (again at constant temperature and pressure). This is because the enthalpy measures the energy that can be extracted from a system, but then we have to subtract TΔS because that energy is released in the form of heat, and the efficiency of a heat engine is zero when both reservoirs are at the same temperature.
8. Gibbs free energy=G=H−TS
9. Gibbs free energy is used to determine the spontaneity of a process.
10. The change in Gibbs free energy for a process is thus written as ΔG delta which is the difference between G-final​ (the Gibbs free energy of the products), and G-initial​ (the Gibbs free energy of the reactants).
11.     ΔG=Gfinal​−Ginitial​

1.     Different scenarios:
•    When ΔG<0, the process is exergonic and will proceed spontaneously in the forward direction to form more products.
•     When ΔG>0, the process is endergonic and will proceed spontaneously in the reverse direction to make more starting materials.
•     When ΔG=0, the system is in equilibrium and the concentrations of the products and reactants will remain constant.
2. Gibbs' Free Energy is generally useful for reactions at constant Temperature and Pressure--which covers a large part of biology and chemistry.
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4. Gibb’s free energy is the energy available in the system to do useful work. It is the difference between the internal energy (sum of all microscopic energy) of the system and the unavailable energy (product of temperature and entropy). By unavailable energy, I mean the energy lost to the surroundings.
5. Change in Gibb’s free energy determines the direction and extent of chemical change. Change in Gibb’s free energy can only be used for systems at constant temperature and pressure. Gibb’s free energy is so famous because almost all the processes and operations operate at constant temperature and p… (more)
6. What are Some of the Applications of the Helmholtz Free Energy?It is often used to derive the equation of state in the case of pure fluids with maximum accuracy for several industrial purposes. The equation state of water can also be obtained from the Helmholtz Free Energy.

The Helmholtz free energy defines the work done that can be extracted from a system with constant temperature and volume; therefore occurs less naturally (since it involves no volume change). The Gibbs Free energy refers to the maximum reversible work that can be extracted from a system in constant pressure and temperature, much like many natural and artificial systems.

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