Final answer:
The chemical reaction described with a ΔG of -30.9 is Exothermic and spontaneous because a negative ΔG indicates the release of free energy, making it an exergonic reaction.
So, the correct answer is A.
Step-by-step explanation:
A chemical reaction with a ΔG (delta G) of -30.9 kcal/mol is described as exergonic and spontaneous. This is because a negative ΔG indicates that the reaction releases free energy, which means the products have less free energy than the reactants. In chemistry, these reactions are categorically known as exergonic reactions, and despite common misconceptions, a spontaneous reaction doesn't necessarily occur quickly; it can happen slowly over time, like the rusting of iron.
Therefore, the correct answer is Exothermic and spontaneous, option A.