Enthalpy (ΔH°): Energy absorbed or released during a reaction. Calculated using Hess's Law: ΔH°rxn = Σ(ΔH°f products) - Σ(ΔH°f reactants)

Entropy (ΔS°): Measure of disorder or randomness. ΔS°rxn = Σ(S° products) - Σ(S° reactants)

Gibbs Free Energy (ΔG°): Determines spontaneity. ΔG° = ΔH° - TΔS°. If ΔG° < 0, reaction is spontaneous.

Equilibrium Constant (K): Ratio of products to reactants at equilibrium. ΔG° = -RT ln(K), so K = e^(-ΔG°/RT)