In a condensation reaction two molecules join together and a small molecule, usually water or hydrogen chloride, is removed.Esterification is a condensation reaction. A carboxylic acid reacts with an alcohol, using concentrated sulfuric acid as a catalyst, to form an ester and water. Ethanoic acid and ethanol form ethyl ethanoate.Esterification is reversible, so an equilibrium mixture forms and the ester has to be separated, for example by distillation.When each monomer has two functional groups, condensation can happen repeatedly to form condensation polymers such as polyesters and polyamides.