text: In chemistry, the ECW model is a semi-quantitative model that describes and predicts the strength of Lewis acid–Lewis base interactions. Many chemical reactions can be described as acid–base reactions, so models for such interactions are of potentially broad interest.  The model initially assigned E and C parameters to each and every acid and base.  The model was later expanded  to the ECW model to cover reactions that have a constant energy term, W, which describes processes that precede the acid–base reaction.  This quantitative model is often discussed with the qualitative HSAB theory, which also seeks to rationalize the behavior of diverse acids and bases.