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We know that in osmosis, the solvent molecules flow from the lower concentration to higher concentration across a semi-permeable membrane. But why do they flow like that?

For my explanation, I took the analogy of water in two vessels at different heights.

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Here we can see that the flow of water is from a higher altitude (and higher gravitational potential) to a lower one. I tried explaining osmosis using the same concept. Since water flows from the solvent side to the solution side, the solvent side must have higher potential energy in some form while the solution side has lower potential energy. But why does solvent have a higher potential than solutions?

The only explanation I can come up with is that when solute molecules like $NaCl$ dissolve, the energy to stabilise $Na+$ and $Cl-$ comes from the solvent itself. But the dissolution of sodium chloride in water is an Endothermic process. There are exothermic dissolution reactions too which doesn't consume energy. So why does solvent have a higher potential than solutions in these cases also?

Adil Mohammed
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The potential you have intuited is called chemical potential. The underlying reason for the osmosis is all about entropy. If the pressures in the two regions are equal, then when the solvent moves, the entropy of the region it enters goes up by more than the amount by which the entropy of the other region falls, so there is a net gain in entropy. Therefore the process will happen spontaneously. An imbalance in pressures can oppose this. The pressure imbalance builds up until the entropy cost of moving solvent in either direction is balanced.

Andrew Steane
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