Gibbs Free Energy Formula

Gibbs Free Energy Formula

The Gibbs Free Energy Formula is given below for the benefit of students.

Gibbs Free Energy

The thermodynamic potential is the Gibbs Free Energy Formula or IUPAC name Gibbs energy or Gibbs function or free enthalpy in thermodynamics. It is used to calculate the maximum reversible work performed by a thermodynamic system at constant pressure and temperature. Furthermore, the Gibbs Free Energy Formula is the thermodynamic potential minimized by a system when it reaches chemical equilibrium at constant temperature and pressure. Also, using the Gibbs Free Energy Formula, one can determine whether a reaction is favourable or unfavourable.

Josiah Willard Gibbs, an American scientist, discovered this property in 1876 while conducting experiments to predict the behaviour of systems when combined or whether a process could occur simultaneously and spontaneously. Gibbs free energy was previously referred to as “available energy.” It can be represented as the amount of useful energy present in a thermodynamic system that can be used to do some work.

Gibbs Free Energy Formula

Gibbs Free Energy Formula is equal to the system’s enthalpy minus the product of temperature and entropy. The equation is as follows:

G = H – TS


or, more precisely;

U + PV – TS = G

Derivation of the formula

In the Formula given above: G=H-TS 

G stands for Gibbs Free Energy Formula.

H stands for enthalpy.

T is for temperature.

S stands for entropy.

In the formula given above : U+PV-TS=G

U denotes internal energy (SI unit: joule)

P stands for pressure (SI unit: pascal)

V stands for volume (SI unit: m3 )

T is for temperature (SI unit: kelvin)

Entropy = S (SI unit: joule/kelvin)

Points relating to Gibbs free energy formula

The following are some Gibbs Free Energy Formula law points:

If G is less than zero, then the products are favoured at equilibrium (K > 1), and the advancing reaction is “thermodynamically favoured.”

If, on the other hand, G is greater than zero, the reactants are favoured at equilibrium, and the advancing reaction is “thermodynamically disfavored.”

A thermodynamically favoured reaction, is sometimes referred to as spontaneous.’ However, this does not guarantee that the reaction will proceed at a detectable rate; high kinetic obstacles can sometimes prevent a reaction from taking place.

We can sometimes determine the sign of G without doing any complicated calculations:

Furthermore, if H is negative and S is positive in a reaction, the reaction is always thermodynamically favoured.

Furthermore, if H is positive and S is negative in a reaction, the reaction is always thermodynamically disfavoured.

Furthermore, if both H and S are either positive or negative in any condition, the thermodynamic favorability of the reaction can be affected by the temperature of the substance.

Most notably, the reactions can be ‘driven by enthalpy’ (in which a very exothermic reaction (negative H) overcomes a decrease in entropy) or ‘driven by entropy’ (in which an endothermic reaction occurs due to a highly positive S).

Solved example for you

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