What does a change in G (deltaG) measure?

The change in Gibbs free energy, denoted as ΔG, is a crucial concept in thermodynamics and chemical reactions as it provides insight into the spontaneity of a process. When ΔG is negative, the reaction or process is spontaneous, meaning it can occur without the input of additional energy. Conversely, if ΔG is positive, the process is non-spontaneous and requires energy input to proceed. This measure not only indicates whether a reaction can take place but also reflects the maximum amount of useful work obtainable from it at constant temperature and pressure.

In essence, ΔG combines both enthalpy and entropy changes within a system, serving as a powerful predictor of how processes will behave under given conditions. Understanding this relationship is vital for analyzing chemical systems and predicting reaction outcomes.