Consider the dissociation reaction A₂(g) ⇌ 2 A(g). The following pictures represent two possible initial states and the equilibrium state of the system:
(b) What are the signs ( + , - , or 0) of ∆H, ∆S, and ∆G when the system goes from initial state 1 to the equilibrium state? Explain. Is this a spontaneous process?

Enthalpy (∆H) is a measure of the total heat content of a system. In a dissociation reaction like A₂(g) ⇌ 2 A(g), if the reaction absorbs heat, it is endothermic, resulting in a positive ∆H. Conversely, if it releases heat, it is exothermic, leading to a negative ∆H. Understanding the sign of ∆H helps determine whether the reaction requires or releases energy.

Entropy (∆S) is a measure of the disorder or randomness in a system. In the reaction A₂(g) ⇌ 2 A(g), the dissociation of one molecule into two increases the number of gas particles, leading to greater disorder. Therefore, this process typically has a positive ∆S, indicating an increase in entropy, which is a driving force for spontaneity in many reactions.

Gibbs Free Energy (∆G) combines enthalpy and entropy to determine the spontaneity of a reaction at constant temperature and pressure. The relationship is given by the equation ∆G = ∆H - T∆S. A negative ∆G indicates a spontaneous process, while a positive ∆G suggests non-spontaneity. Evaluating the signs of ∆H and ∆S is crucial for predicting the sign of ∆G and the spontaneity of the reaction.