During a chemical reaction, the Gibbs free energy varies with concentration, as it is influenced by the concentrations of both reactants and products.

The Gibbs free energy, denoted as $G$, is a thermodynamic potential that quantifies the maximum reversible work a system can perform at constant temperature and pressure. Being a state function, its value is determined solely by the state of the system, independent of the path taken to reach that state. In the context of a chemical reaction, the change in Gibbs free energy, represented as $\Delta G$, is directly related to the concentrations of the reactants and products involved.

The relationship between Gibbs free energy and concentration is expressed by the equation:

where:

• $\Delta G^\circ$ is the standard Gibbs free energy change,
• $R$ is the universal gas constant,
• $T$ is the absolute temperature measured in Kelvin,
• $Q$ is the reaction quotient, which reflects the relative concentrations of the products and reactants at any given moment during the reaction.

When a reaction reaches equilibrium, the reaction quotient $Q$ becomes equal to the equilibrium constant $K$, and at this point, $\Delta G$ is zero. This condition signifies that there is no net change occurring in the system, meaning no work can be extracted from the reaction. If $Q$ is less than $K$ (indicating a higher concentration of reactants compared to products), $\Delta G$ will be negative, suggesting that the reaction is spontaneous in the forward direction. Conversely, if $Q$ exceeds $K$ (indicating a higher concentration of products than reactants), $\Delta G$ will be positive, indicating that the reaction is non-spontaneous in the forward direction but spontaneous in the reverse direction.

In summary, the change in Gibbs free energy during a reaction is dependent on the concentrations of the reactants and products. It can be calculated using the equation:

and the sign of $\Delta G$ indicates the direction of spontaneity for the reaction. Understanding this relationship is essential for predicting the behavior of chemical reactions.