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## Main Question or Discussion Point

Wikipedia says :

In thermodynamics, the Gibbs free energy (IUPAC recommended name: Gibbs energy or Gibbs function; also known as free enthalpy[1] to distinguish it from Helmholtz free energy) is a thermodynamic potential that measures the "useful" or process-initiating work obtainable from a thermodynamic system at a

So is gibbs free energy only valid for constant pressure and temperature?

I tried to find change in gibbs free energy of a chemical reaction under these conditions and it always comes zero.

ΔG = ΔH - TΔS ..... temperature is constant

ΔG = ΔH - TΔH/T..... at constant pressure q = ΔH

ΔG = 0

there is something wrong in this as reactions do happen at constant pressure and temperature adn gibbs free energy change is not zero

In thermodynamics, the Gibbs free energy (IUPAC recommended name: Gibbs energy or Gibbs function; also known as free enthalpy[1] to distinguish it from Helmholtz free energy) is a thermodynamic potential that measures the "useful" or process-initiating work obtainable from a thermodynamic system at a

**constant temperature and pressure**(isothermal, isobaric).So is gibbs free energy only valid for constant pressure and temperature?

I tried to find change in gibbs free energy of a chemical reaction under these conditions and it always comes zero.

ΔG = ΔH - TΔS ..... temperature is constant

ΔG = ΔH - TΔH/T..... at constant pressure q = ΔH

ΔG = 0

there is something wrong in this as reactions do happen at constant pressure and temperature adn gibbs free energy change is not zero