Gibbs Free Energy : Definition of Gibbs Free Energy

Gibbs Free Energy (G) – The energy combined with a chemical reaction can be used in chemical work. The free energy of a system is the entirety of its enthalpy + the product of the temperature (Kelvin) and the system’s entropy: The reaction’s free energy.

Equation :

The change in Gibbs Free Energy  is caused by constant heat and pressure and defines as ΔG = ΔH-TΔS. As the heat and pressure are unchangeable, the T remains constant. ΔG = change in Final and initial Gibbs energy, ΔS = change in final, and Enthalpy of the system.

Symbol :              

The symbol is symbolized as ‘G.’

To get an overview of Gibbs’s energy and its general uses in chemistry, Gibbs Free Energy , denoted G, and combines enthalpy and entropy into a single value. The change in free energy is ΔG, which is equal to the enthalpy’s sum plus the system’s temperature and entropy product.

Purpose :

The Gibbs Free Energy  is one of the essential thermodynamic functions for the characterization of a system. It is a multiplier in realizing outcomes such as the voltage of an electrochemical cell, and the equilibrium constant for a reversible reaction.

What does Gibbs’s free energy tell us?

It is the maximum amount of non-valuable work that can be extracted from a thermodynamically closed system (can exchange heat and work with its surroundings, but no matter). This maximum can be performed only in a completely reversible process.

The physical significance:-

According to the first law of thermodynamics,

ΔU = q – w

 Here, q is the heat absorbed by the system, and w is the work done by the system, while Δu is the change in initial energy. The work (w) includes two types of work, the two types of works can be understood by taking an example of the electrolysis of water to form Hydrogen and Oxygen, leading to an increase in the system’s volume. The work non-expansion (non-mechanical) is done to cause the decomposition of water while the work expansion is due to expansion in the volume of the system. Thus, the electrical work is called non-pressure-volume work or non-expansion work, or non-mechanical work. The non-expansion work is also known as useful work.

The greater the free energy change, the greater the amount obtained from the process. This relation is useful in assessing the electrical work produced by electrochemical cells and fuel cells.

Free Energy change and electrical work are done cells :

The following relation relates ΔG and emf of the cell €:

                           ΔG = – nFE

Where,    F = faraday = 96500 coulomb

              E = emf of the cell

              n = Number of moles of celetrones involved in a balanced electrochemical reaction

If the reactants and products are their standard states, then

               ΔG degree = -nFE degree

When E degree = standard emf of the cell.

In constant pressure and temperature, the change of Gibbs Free Energy  of any process :

The change of Gibbs Free Energy  in a process with constant pressure and temperature is ΔG = ΔH – TΔS.

(Though T is constant, so Δ(TS) = TΔS)……..(!)

This (1) equation means the relation between the change of enthalpy, the entropy of the system, and T under the constant pressure and temperature condition. 

By the equation, anyone can decide if this process is spontaneous. In constant pressure and temperature in any chemical or physical change, the change of Gibbs Free Energy  is less than zero.

Then the process will be spontaneous. In constant pressure, temperature, and pressure in any chemical or physical change of Gibbs, free energy is more significant than zero. This process will not be spontaneous, but the opposite process will be spontaneous. Gibbs Free Energy  is a state function.


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