Question

Explain what is wrong with the following statement: At any given temperature, only a single phase with the lowest Gibbs free energy is observed.

Answer 1

The Gibbs Phase Rule states that the number of degrees of freedom is 2 plus the number of components minus the number of phase, i.e., DF= 2 + c - pi

1. An intensive variable is one which does not depend on system size (like temperature, pressure, or specific volume). Gibbs free energy is one of the intensive variables
2. G is commonly called Gibbs free energy. It is a measure of the stored energy in a reaction. Gibbs free energy is the amount of energy left over after a chemical reaction has taken place.
3. Gibbs proposed that all spontaneous physical and chemical changes take place in the direction of a decrease in free energy.
4. A spontaneous reaction may involve an increase or decrease in enthalpy, it may involve an increase or decrease in entropy, but it will always involve a decrease in free energy that is a negative ΔG.
5. When ΔG is negative, the reaction would go in the direction of reactants forming products and not in the reverse direction.

At any given temperature a single phase is never observed when the Gibbs free energy is present. It is the equilibrium of the two phases which makes it seem as single phase.

At lowest Gibbs free energy the system whatever may be the number of components will be in equilibrium.