Introduction

Gibbs free energy, also known as the Gibbs function, or Gibbs energy, is used to estimate the maximum work possible in a thermodynamic system if the temperature and pressure remain constant. The ‘G’ symbol stands for Gibbs’s energy. Joules or Kilojoules are commonly used to express their worth.

Josiah Willard Gibbs, an American scientist, discovered this phenomenon in 1876 while performing experiments to anticipate the behaviour of systems when they are combined or whether a process can happen concurrently and spontaneously. The term “available energy” was previously used to refer to Gibbs’s energy. 

As a general rule, the total energy difference primarily determines how spontaneous a process is. We may say that enthalpy and entropy have changed over time as most chemical processes belong to either the closed or open categories of systems.

Gibbs free energy formula

The enthalpy of the system, excluding the temperature and entropy product, equals Gibbs’ free energy.

The equation is as follows:

H – TS = G

Where,

T is for temperature

G stands for Gibbs free energy

H stands for enthalpy

S stands for entropy

OR

Or to a greater extent;

U + PV – TS = G

Where,

U stands for internal energy (SI unit: joule)

P stands for pressure (SI unit: pascal)

V stands for volume (SI unit: m3)

T stands for temperature (SI unit: kelvin)

(SI unit: joule/kelvin) S = entropy

The Equation’s variations

Because Gibbs energy is a state function, it is independent of the path. As a result, the change in Gibbs free energy = the enthalpy change minus the product of the temperature and entropy changes in the system.

ΔG = ΔH – Δ (TS)

If the reaction takes place at a constant temperature {ΔT=0}

ΔG = ΔH – TΔS

The Gibbs Helmholtz equation is the name given to this equation.

ΔG > 0; the reaction is endergonic as well as non-spontaneous.

ΔG< 0; the reaction is exergonic as well as spontaneous.

ΔG = 0 indicates equilibrium reaction.

Spontaneous process:  Spontaneity does not entail that the reaction happens quickly. Natural processes, such as the degradation of diamonds into graphite, take millions of years. The reaction’s rate is determined by the chemical kinetics of the reaction rather than its spontaneity. In a spontaneous process, every reactant tends to generate the matching product. This pattern is linked to stability.

Non-spontaneous process: A chemical reaction in which the sample in free energy is positive while energy is absorbed is known as an endergonic reaction (also known as a non-spontaneous reaction or an unfavourable reaction). The overall quantity of energy is a loss (it takes more energy to initiate the reaction than it gives back); hence the total energy is negative. It is possible to accelerate endergonic reactions by connecting them through a shared intermediate to a strongly exergonic reaction.

Note:

• As per the second rule of thermodynamics, entropy in the cosmos always grows for a spontaneous process.

• ΔG determines the direction and extent of chemical change.
• Only reactions in which the temperature and pressure remain constant are relevant to ΔG. We start and conclude the operation at room temperature, and the system is usually open to the atmosphere (constant pressure) (after any heat we have added or which is liberated by the reaction has dissipated).
• The single master variable ΔG decides whether a chemical change is thermodynamically viable. As a result,if the reactants’ free energy is greater than the products’, entropy of this process increases and the process will tend to occur spontaneously. The ΔS universe is made up of the ΔS system, and the ΔS surrounds. If ΔG is negative, the process will happen on its own and is known as exergonic.
• As a result, spontaneity is influenced by the system’s temperature.

Keep this in mind

For predicting spontaneity, free energy change parameters are better than entropy change criteria since the former just requires free energy change in the system, while the latter requires entropy change.

Gibbs energy formula

We may rearrange the second rule of thermodynamics and establish a new number known as Gibbs free energy, also called Gibbs energy, when a process happens at constant temperature T and pressure P.

                        Gibbs energy = △G = △H – T△S

H stands for enthalpy.

T is for temperature.

S stands for entropy.

Gibbs free energy is spontaneous

The direction in which total entropy grows is the direction of spontaneous change. Total entropy change, often known as the entropy change of the universe, is the total of a system’s and its surrounds’ entropy changes:

                                                               △S (sys) + △S (surr) = △S (univ)

S (univ) must always rise for a spontaneous process, according to the second law of thermodynamics, the entropy of the cosmos, △S (univ) > 0

Conclusion

Gibbs energy is a state function with a wide range of applications. Since entropy change influences molecular movement, it cannot explain how such a phenomenon occurs spontaneously. As a result, the Gibbs energy change is used to explain the spontaneity of a process. Spontaneity does not entail that the reaction happens quickly. Diamond degradation into graphite, for example, is a naturally occurring process that takes millions of years to complete.  A chemical reaction in which the sample in free energy is positive while energy is absorbed is known as an endergonic reaction. We may rearrange the second rule of thermodynamics and establish a new number known as Gibbs free energy, also called Gibbs energy, when a process happens at constant temperature T and pressure P.