What You’ll Learn

Hess's Law states that the enthalpy change (ΔH) for a reaction is independent of the pathway and only depends on the initial and final states. Similarly, the equilibrium constant (K) for a reaction can be determined from the equilibrium constants of coupled reactions, even if the overall reaction has not been directly studied. The relationship is that the equilibrium constant for the overall reaction is equal to the product of the equilibrium constants for the individual coupled reactions. This multiplicative relationship for equilibrium constants contrasts with the additive relationship for enthalpy changes according to Hess's Law.