At chemical equilibrium, the Gibbs function is zero. The Gibbs function, also known as the Gibbs free energy or Gibbs energy, is a thermodynamic potential that measures the maximum reversible work that can be performed by a system at constant temperature and pressure. It is denoted by the symbol G.

The Gibbs function is defined as:

G = H - TS

Where:
- G is the Gibbs function
- H is the enthalpy of the system
- T is the temperature
- S is the entropy of the system

When a chemical reaction reaches equilibrium, it means that the rates of the forward and reverse reactions are equal, and there is no net change in the concentrations of reactants and products. At equilibrium, the system has reached a state of minimum free energy, and the Gibbs function is at its minimum value.

Explanation:
1. At equilibrium, the forward and reverse reactions are occurring at the same rate.
2. The system has reached a state of minimum free energy. This means that the system has achieved the most stable configuration possible under the given conditions.
3. If the Gibbs function were not zero at equilibrium, the system would be able to spontaneously undergo a change to decrease its free energy further. This would violate the principle of equilibrium, where there is no net change in the system.
4. The Gibbs function is a measure of the potential to do work. At equilibrium, the system has used up all of its potential to do work, and the Gibbs function is zero.
5. The Gibbs function can be thought of as a balance between the enthalpy (H) and entropy (S) of the system. At equilibrium, the enthalpy and entropy contributions cancel each other out, resulting in a zero Gibbs function.

In conclusion, at chemical equilibrium, the Gibbs function is zero. This indicates that the system has reached a state of minimum free energy and has used up all of its potential to do work.