What does a negative Δ G indicate about a reaction?

A negative ΔG, or Gibbs free energy change, indicates that a reaction is spontaneous and can proceed without the input of external energy. This characteristic often implies that the reaction can release energy, which is why it is considered exergonic. When ΔG is negative, the products of the reaction have lower free energy than the reactants, resulting in a release of energy as the reaction moves forward.

In contrast, a reaction that requires energy to proceed would have a positive ΔG, which shows that the products have higher free energy than the reactants. Similarly, a reaction at equilibrium would have a ΔG of zero, indicating no net change in free energy, whereas a requirement for heat addition doesn't directly relate to the free energy change but rather pertains to thermodynamic conditions that might influence reaction rates and pathways.