What does a ΔG value less than 0 signify about a thermodynamic process?

A ΔG value less than 0 indicates that a thermodynamic process is spontaneous. The Gibbs free energy change (ΔG) is a measure of the amount of usable work obtainable from a thermodynamic system at constant temperature and pressure. When ΔG is negative, it signifies that the process can occur without the need for additional energy input, meaning that the system is moving towards a more stable state. This favorable change in free energy implies that the system can perform work as it transitions from its initial state to a final state.

In practical terms, a negative ΔG means the reaction can proceed forward, leading to its products without requiring external energy, hence producing work in the process. This is particularly important in understanding chemical reactions and other thermodynamic processes as it informs the feasibility of such reactions occurring under the given conditions.