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Gibbs Free Energy
This is another thermodynamic quantity that helps in predicting the spontaneity of a process, is called Gibbs energy (G).
It is defined mathematically by the equation.
G = H - TS
Where H = heat content, S = entropy of the system, T = absolute temperature
Solved example: Which of the following will fit into the blank?
When two phases of the same single substance remain in equilibrium with one another at a constant P and T, their molar _________ must be equal.
(A) Internal energy (B) Enthalpy
(C) Entropy (D) Free energy
Free energy change
For isothermal process.
ΔG = G2 – G1 = ΔH – TΔS
ΔG = change in Gibbs free energy of the system.
It is that thermodynamic quantity of a system the decrease in whose value during a process is equal to the maximum possible useful work that can be obtained from the system.
Solved example: Calculate free energy change when one mole of NaCl is dissolved in water at 25°C. Lattice energy = 700 kJ/mol.ΔS at 25°C = 26.5 Jmol–1, Hydration energy of NaCl = -696 kJ/mol.
(A) -3.9 kJ (B) -8kJ
(C) -12kJ (D) -16kJ