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Where does the energy come from to lift water by osmosis? (feddit.uk)

submitted 3 weeks ago* (last edited 3 weeks ago) by Robbo@feddit.uk to c/asklemmy@lemmy.ml

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For example in a tree, the water is lifted from the high concentration in the soil to the low concentration higher up in the tree. But at the end of that process the water has been elevated, which should take energy (=mgh), but it seems like it kind of gets lifted for free without spending any energy?

Similarly, dipping a paper towel into a bowl of water, the water "climbs" the towel (by capillary action?) and absorbs upwards, meaning the water was lifted upwards (so gained potential energy) seemingly for free?

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[–] GrappleHat@lemmy.ml 2 points 3 weeks ago

I don't remember all of the details, but I thought it was essentially the water's surface tension that foots the energy bill when climbing a paper towel or a capillary in a tree.

The surface of fluids like water are unhappy. Molecules on the surface would much rather be deep in the fluid because on the surface they have "dangling" Van der Waals & polar bonds to one side. You can calculate the potential energy of the surface due to all of those dangling weak bonds, & that's the energy that is used to climb a capillary (the energy isn't free).

I could be misremembering though, I admit. School was many years ago...