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Surface Energy

The molecules on the liquid surface experience net downward force. So to bring a molecule from the interior of the liquid to the free surface, some work is required to be done against the intermolecular force of attraction, which will be stored as potential energy of the molecule on the surface. The potential energy of surface molecules per unit area of the surface is called surface energy.
Unit: Joule/m2 (SI) erg/cm2 (CGS)
Dimension: [MT–2]
Surface tension may be defined as the amount of work done in increasing the area of the liquid surface by unity against the force of surface tension at constant temperature.
Work done in blowing a liquid drop or soap bubble If the initial radius of liquid drop is r1 and final radius of liquid drop is r2, then
W = T × Increment in surface area
T × 4π (r22 – r12)
[drop has only one free surface]
In case of soap bubble,
W = T × 8π (r22 – r12)
[bubble has two free surfaces]

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