Gibb’s Free Energy

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Thermodynamic variable that is crucial for forecasting the spontaneity of chemical reactions is Gibb’s Free Energy (G). This was discovered by American physicist Josiah Willard Gibbs, and uses the system’s temperature (T), entropy (S), and enthalpy (H) to determine that a reaction will occur spontaneously or need outside energy
In simple form, Gibb’s Free Energy give idea on the viability and course of chemical reactions that occur under constant pressure and temperature.

Formula for Gibb’s Free Energy:-


Gibb’s Free Energy is mathematicallyexpressed as:
G = H − TS
Where:
G is the Gibb’s Free Energy,
H is the enthalpy of the system,
T is the temperature in Kelvin,
S is the entropy of the system
Formula shows the relationship between a system’s heat content and the energy that is available inside it. The disordered energy is denoted by the  TS, and the total energy accessible is denoted by the H.

Spontaneity:-

The sign of ΔG, or change in Gibb’s Free Energy, indicates how spontaneous a reaction is.
  • ΔG < 0: Reaction is spontaneous. It will proceed without the need for external energy.
  • ΔG > 0: Reaction is non-spontaneous. It requires external energy to proceed.
  • ΔG = 0: Reaction is at equilibrium. There is no net change in the system.
Reaction’s spontaneity is dependent upon not just the enthalpy change (ΔH) but also the temperature (T) at which it takes place, as well as the entropy change (ΔS).

Enthalpy, Entropy, and Gibb’s Free Energy:-

1. When ΔH is Negative (Exothermic Reaction) and ΔS is Positive (Increase in Disorder):
In this case, the reaction is spontaneous at all temperatures since ΔG will always be negative.
Example:  Combustion of methane
(CH4+2O2→CO2+2H2O) This reaction releases energy (negative ΔH) and increases the disorder (positive ΔS), making it spontaneous.
2. When ΔH is Positive (Endothermic Reaction) and ΔS is Negative (Decrease in Disorder):
In this case, reaction is not spontaneous at any temperature since ΔG will be positive.
Example: Under normal circumstances, nitrogen and oxygen react to generate nitrogen dioxide (N2+O2→2NO2). Reaction is non-spontaneous since it requires energy input (positive ΔH) and produces a decrease in disorder (negative ΔS)..
 3. When ΔH is Negative and ΔS is Negative:-
Temperature affects the spontaneity. Because of the dominance of the negative ΔH at low temperatures, ΔG is negative (spontaneous). At high temperatures, however, ΔG may become positive (non-spontaneous) due to the dominance of the negative TS. 
Example: Water freezes spontaneously (negative ΔG) below 0°C and non-spontaneously above 0°C.
Thermodynamics-Ice
Ice
4. When ΔH is Positive and ΔS is Positive:
ΔG is positive in this case, the reaction is not spontaneous at low temperatures. At high temperatures, however, the TS has the ability to turn ΔG negative, resulting in an uncontrollable reaction.
Example: Ice melts spontaneously (positive ΔH and positive ΔS) above 0°C and non-spontaneously below 0°C..

Applications of Gibb’s Free Energy:-

Gibb’s Free Energy is important to many industrial and scientific activities.
Biological Systems: Gibb’s Free Energy is useful in biological systems to understand how cells store and use energy during activities like ATP generation..
Chemical Engineering: Idea is applied in chemical engineering to ensure that chemical reactions are carried out inexpensively and efficiently.
Phase Transitions: Gibb’s Free Energy also analyses the temperature dependence of the spontaneity to explain phase changes, as the boiling or melting of ice..

Note:–

A useful method for determining the course and possibility of chemical processes is Gibb’s Free Energy. Temperature, entropy, and enthalpy are combined to give a complete picture of how energy moves inside a system. A fundamental idea in thermodynamics and chemistry, Gibb’s Free Energy is useful for understanding phase transitions, forecasting the spontaneity of a reaction, and streamlining industrial operations.
Thermodynamic term called Gibb’s Free Energy (G) is used to forecast if a chemical reaction will happen on its own at constant pressure and temperature. It determines the direction and feasibility of a reaction by combining the system’s enthalpy, entropy, and temperature.
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Formula G = H − TS is used to determine Gibb’s Free Energy, where H stands for enthalpy, T for temperature in Kelvin, and S for system entropy. The spontaneity of a reaction is determined by the change in Gibb’s Free Energy (ΔG).
When the chemical reaction is spontaneous that’s able to happen without the need from outside energy it has a negative ΔG. Naturally, the system moves in the direction of least Gibb’s Free Energy.
Yes, if the temperature is high enough for the TS  to dominate the positive ΔH and produce a negative ΔG, a reaction can still be spontaneous even if the change in enthalpy (ΔH) is positive.
Determination of Gibb’s Free Energy is considerably influenced by temperature. The importance of the entropy TS increases with temperature. If both ΔH and ΔS are positive, this can cause a reaction that is not spontaneous at low temperatures to become spontaneous at higher temperatures.
Gibb’s Free Energy is a crucial concept in biological processes because it helps us to understand how cells use energy. For example, cells use the energy released during the hydrolysis of ATP (which has a negative ΔG) to power a many functions, including chemical synthesis and muscular contraction.
Reaction is at equilibrium when ΔG = 0. This indicates that the forward and reverse reactions happen at the same pace and that there is no net change in the system. There is no external force pushing the reaction in either direction, hence the system is in a condition of equilibrium.

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