How does capillary action pulling a fluid up a narrow tube result in a more stable state than if the fluid stayed at the same level?

Question

Essentially, how does capillary action obey entropy? Why does the fluid stop at a certain point up the tube?

In: Chemistry

Answer 1

Molecules are made of highly electrically charged particles and all interact with each other like little magnets. Some are attracted to each other, some strongly repel, and some are indifferent and neutral.

When a liquid is climbing up the inside of a narrow tube, that’s an indication that the liquid molecules are more attracted to the tube wall molecules than they are to eachother. They’re quite literally climbing all over eachother trying to touch the wall as that’s the more optimal energy state.

But! As the liquid column grows, so too does the force of gravity. The low energy bonus the molecules are getting by touching the tube is eventually offset by the sheer weight of the column and it can climb no higher.

Climbing up the tube is increasing the surface area of the liquid, which typically means an increase in system entropy.