The displacement velocity of each crystalline face of aspirin on dissolution in distilled water was determined by using large single crystals grown from ethanolic solution. It was found that each crystalline face of aspirin has its own displacement velocity. The specific surface energies for those crystalline surfaces in water and in vacuo were calculated from a set of atom-atom pairwise potential functions. The relative rate of diminution of surface area on dissolution of the crystal can be correlated to the sensitivity of the surface energy to the polarity of the solvent.