and are the energy of cohesion and are always a negative quantity for a condensed phase. is the energy of adhesion. Therefore, Eq. (2.7) can be rewritten as

To use this equation we should have knowledge of the pair-wise interaction between molecules. Eq. (2.8) can be simplified further as discussed below.

Suppose medium 2 is an inert gas. In that case the term and can be neglected because there will be very few molecules of 2 at the surface to have any significant effect.

		(2.9)

Similarly if 2 is the condensed phase

		(2.10)

Now Eq. (2.8) can be rewritten as

(2.11)

where, is the energy of adhesion, and and are the energies of cohesion of the two materials.