How can you identify whether a chemical reaction is spontaneous?

To determine whether a chemical reaction is spontaneous, assessing Gibbs free energy changes is the most reliable method. Gibbs free energy is a thermodynamic potential that helps predict the direction of chemical processes at constant temperature and pressure. A reaction is considered spontaneous if the change in Gibbs free energy (ΔG) is negative. This indicates that the products of the reaction have lower energy than the reactants, making the reaction favorable and able to occur without external energy input.

While measuring temperature changes might provide some insight into the energy dynamics of the reaction, it alone does not comprehensively indicate spontaneity. Observing color changes or other physical changes can be part of monitoring a reaction, but they do not give the quantitative assessment needed to determine spontaneity. Only changes in Gibbs free energy provide a definitive criterion for spontaneity in a broader range of reactions, making it the correct approach among the given options.