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I have that a book that says "Low surface tension of a liquid helps it to spread over a larger area." . My question is How and Why ? When I say that a liquid A has a lower surface tension than liquid B , does that mean that the cohesive forces and the force with which molecules of liquid A pulls other molecules towards themselves for A are less than that of B ?

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  • $\begingroup$ I don't think so , but if you know the answer , (a hint would do) , a little help would be appreciated $\endgroup$ – user82731 Dec 16 '15 at 11:17
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There are two types of intermolecular forces:

1) Cohesive forces: Intermolecular forces (such as those from hydrogen bonding and Van der Waals forces) which cause a tendency in liquids to resist separation. These attractive forces exist between molecules of the same substance

2) Adhesive Forces: Attractive forces between unlike molecules. They are caused by forces acting between two substances, such as mechanical forces (sticking together) and electrostatic forces (attraction due to opposing charges)

A liquid with low cohesive attraction and more adhesive attraction has a low surface tension. It sticks more to the container or surface than to itself(like benzene) and spreads itself as much as possible. Whereas mercury has high surface tension and forms balls when left on a smooth surface, in effect reducing its surface area.

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  • $\begingroup$ So when one says that a liquid A has a lower surface tension than liquid B , does that mean that the cohesive forces of liquid A are less than liquid B ?(I have made an edit to my question , kindly answer to the added query ; your help is appreciated.) $\endgroup$ – user82731 Dec 16 '15 at 11:21
  • $\begingroup$ Also , the book that I have defines surface tension as : "The property of a fluid by virtue of which the free surface of a liquid at rest behaves like an elastic stretched membrane tending to contract so as to occupy minimum surface area." . Can you please explain how your definition supports the one in my book ? $\endgroup$ – user82731 Dec 16 '15 at 11:33
  • $\begingroup$ The answer to the added query is yes. Surface tension is an indirect measure of the difference between the cohesive and adhesive forces, So how much is the cohesive force more than the adhesive force. An increase in cohesive force makes the liquid want to minimize its surface area as the net force is acting towards the center of the liquid. $\endgroup$ – Hemang Rajvanshy Dec 16 '15 at 11:55
  • $\begingroup$ So , if I pour a liquid which has high surface tension(A) over a liquid which has comparatively lower surface tension(B) , will A spread over B (I think it won't but I cannot convincingly answer this question.) $\endgroup$ – user82731 Dec 16 '15 at 12:10
  • $\begingroup$ It won't because it does not wish to increase its surface area. $\endgroup$ – Hemang Rajvanshy Dec 19 '15 at 12:35

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