Final answer:
A negative ΔG value indicates spontaneity in a reaction. Spontaneity can also be predicted by examining the signs of enthalpy (ΔH) and entropy (ΔS) changes, and combining them with the understanding that temperature (T) in the Gibbs free energy equation is always positive. When ΔH is negative and ΔS is positive, the reaction will be spontaneous at all temperatures.
Step-by-step explanation:
A spontaneous reaction is one that proceeds without the need for continuous input of energy from an external source. The spontaneity of a reaction is determined by the Gibbs free energy change (ΔG), which can be calculated using the equation ΔG=ΔH-TΔS, where ΔH is the change in enthalpy, T is the absolute temperature in Kelvin, and ΔS is the change in entropy. A negative ΔG value indicates a spontaneous process, a positive ΔG indicates a nonspontaneous process, and a ΔG of zero indicates that the system is at equilibrium.
Furthermore, the signs of enthalpy (ΔH) and entropy (ΔS) changes can also predict spontaneity: when ΔH is negative and ΔS is positive, ΔG will always be negative, indicating spontaneity at all temperatures. Conversely, when ΔH is positive and ΔS is negative, ΔG will always be positive, and the reaction will never be spontaneous. The product of temperature and ΔS can influence the spontaneity if ΔH and ΔS have the same signs.
These principles help to determine whether a process is endothermic or exothermic, whether it is associated with an increase in entropy or a decrease, and whether a process is spontaneous, non-spontaneous, or at equilibrium.