A molecule situated well inside a liquid experiences intermolecular attractions from all directions, whereas a molecule near the free surface experiences an unbalanced inward attraction. Which statement best explains the physical origin of surface tension?
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Question

A molecule situated well inside a liquid experiences intermolecular attractions from all directions, whereas a molecule near the free surface experiences an unbalanced inward attraction. Which statement best explains the physical origin of surface tension?

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G1 Physics · Accepted Answer

A molecule in the bulk is surrounded by neighbouring molecules in all directions, so the intermolecular attractions are nearly balanced. A molecule near the free surface has fewer neighbouring molecules on the outer side and therefore experiences a net inward attraction. Work must be done to bring molecules from the bulk to the surface. Hence molecules at the surface possess excess potential energy. A liquid therefore tends to minimize the number of surface molecules and consequently tends to m…