The formation of an ester from a carboxylic acid and an alcohol is called esterification. The mechanism of esterification is a nucleophilic acyl substitution reaction, which occurs in several steps:1. Protonation of the carbonyl oxygen: The carboxylic acid donates a proton H+ to the carbonyl oxygen, making it more electrophilic. This step is facilitated by the presence of an acid catalyst, such as sulfuric acid H2SO4 or hydrochloric acid HCl .2. Nucleophilic attack: The alcohol, acting as a nucleophile, attacks the electrophilic carbonyl carbon, forming a tetrahedral intermediate.3. Proton transfer: A proton from the alcohol's hydroxyl group is transferred to the oxygen atom that was originally part of the carbonyl group. This step generates a good leaving group, which is a water molecule.4. Elimination of the leaving group: The oxygen atom that received the proton in the previous step donates its electrons back to the carbonyl carbon, reforming the carbonyl double bond C=O . Simultaneously, the water molecule the leaving group is eliminated.5. Deprotonation: The ester product is deprotonated by the conjugate base of the acid catalyst, regenerating the acid catalyst and yielding the final ester product.Overall, the reaction can be summarized as:Carboxylic acid + Alcohol + Acid catalyst Ester + Water + Acid catalystThis reaction is reversible, and the equilibrium can be shifted towards ester formation by using an excess of one of the reactants usually the alcohol or by continuously removing the water produced during the reaction.