Why do surface layer molecules have higher potential energy than molecules inside a liquid?

When the surface of the liquid increases due to external action, some of the molecules from the inner regions of the liquid are transferred to its surface. With such a transition, work is performed against the forces of attraction acting on the molecules passing into the surface layer. It is known from mechanics that when performing work against the forces of attraction, the potential energy of the body being moved increases. Therefore, molecules on the surface of a liquid have more energy than the same molecules inside a liquid.