In the preparation of esters, it is important to keep the volumes of the chemicals constant to ensure that the reaction proceeds efficiently and yields the desired product. This is because the chemical reaction that produces esters is a type of equilibrium reaction, meaning that it can reach a state of balance between the reactants and products.
If the volumes of the chemicals are not kept constant, then the ratio of reactants will change, and this can affect the equilibrium of the reaction. For example, if the volume of the alcohol used is increased, then the reaction may shift towards the reactants, and less ester will be produced. On the other hand, if the volume of the acid is increased, then the reaction may shift towards the products, and an excess of ester may be produced.
Therefore, to ensure that the reaction proceeds as planned and yields the desired amount of product, it is necessary to keep the volumes of the chemicals constant. This helps to maintain the proper ratio of reactants, which in turn affects the equilibrium of the reaction and the yield of the ester.