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Q & A: exothermic wetting and absorption

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Most recent answer: 01/11/2014
Q:
Why does water (or moisture) absorption to some materials (such as some dry synthetic fibers, superabsorbent polymers?, some kind of fine powder? etc.) increase temperature (or heat)? How is the molecular kinetic energy increased in the phenomenon? Which molecules (fiber, water, or/and air?) receive energy from where (potential energy? stored originally where)?
- Anonymous
A:

Here's the main effect. The surfaces of many materials have fixed electrical charges on them. There's some potential energy in the  electric field around each of those charges. Water molecules reduce those fields by arranging their positive charges (the H's) and negative (the O's) to partly line up in the fields. That lost electrostatic energy shows up as thermal energy, raising the temperature. This thermal energy partly takes the form of kinetic energy of the motion of the molecules. Partly it takes the form of potential energy, in effect compression and stretching of the spring-like contacts between the molecules as they jiggle around.

Mike W.


(published on 01/11/2014)

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