What does a negative ΔG indicate about a chemical reaction?

A negative ΔG, or Gibbs free energy change, signifies that the reaction can occur spontaneously under the given conditions. This means that the total energy of the products is lower than that of the reactants, indicating that the reaction can proceed in the forward direction without the need for additional energy input from an external source.

In the context of thermodynamics, spontaneous reactions are those that naturally occur without being driven by an ongoing input of energy, meaning they can reach completion over time. While it is important to note that a negative ΔG does not imply that the reaction occurs quickly, it does indicate that the reaction is favorable under standard conditions.

In this case, the idea of a reaction being at equilibrium would suggest that there is no net change occurring, which is characterized by a ΔG of zero. Non-spontaneous reactions would have a positive ΔG, requiring energy to proceed, and an endothermic reaction is defined by its heat exchange rather than Gibbs free energy, as it can have either a positive or a negative ΔG depending on the overall energy changes involved in the reaction. Therefore, a negative ΔG is a clear indicator of spontaneity in a chemical reaction.