At a molecular level, explain why, in osmosis, there is a net migration of solvent from the side of the membrane less concentrated in solute to the side more concentrated in solute.

Within the invisible battlefields of one's cells, the semipermeable membrane plays a crucial role similar to a gatekeeper. It's a thin barrier that separates different fluid compartments and, like a meticulous security guard, decides which molecules are allowed to enter or exit.

Imagine placing a drop of ink into a glass of water. You will observe the ink slowly dispersing until the whole glass is uniformly colored. Now, think of a semipermeable membrane as a filter between two such glasses of water – one with ink and one without. The membrane allows only the water (solvent) to mix with the ink (solute), not the other way around. This meticulous selection process, underpinning osmosis, is a result of tiny pores that only admit molecules that are small enough, like water, while rejecting larger ones, like sugar or salt.

Just like humans tend to meander from a cramped room to an airy space, molecules innately move from a place of crowding (high chemical potential) to spacious freedom (low chemical potential). Chemical potential signals a great escape, a quest for balance where molecules traverse until they feel an even spread of personal space – or in scientific terms, until chemical potential is equal on both sides of a membrane.

During osmosis, water's tiny molecules feel this imbalance and hustle through the semipermeable membrane from the less crowded area (low solute concentration) to the mosh pit of solute (high solute concentration). Their objective? Homogenize their energy levels until the 'room' on both sides of the membrane feels equally comfortable.

Entropy is the life of the party, where molecules revel in randomness and chaos. The second law of thermodynamics dictates that within an isolated system, such as our universe, things tend to go from orderly to disorderly – it's the natural flow towards maximum entropy.

How does this tie into osmosis? When solvent molecules shuffle from one compartment to another, they are actually following the universe's rule of disorder. With osmosis, water chooses to disperse and create a mixed, broadly distributed crowd rather than a segregated one. This increase in entropy is nature's subtle way of inviting all molecules to the dance floor, ensuring no wallflowers are left behind a semi-impermeable barrier.

While entropy invites everyone to the dance, osmotic pressure is the bouncer determining who actually makes it through the door. Analogous to the push you feel when trying to merge into a packed subway car, osmotic pressure is the force exerted when solvent molecules jostle to pass through the semipermeable membrane toward a higher concentration of solute.

To picture this, envision a crowd surging towards a concert hall but encountering a door that only lets a few in at a time; osmotic pressure equates to that push from behind. It's the measure of just how badly the solvent wants to move across the membrane to balance concentration levels. If we were to apply external pressure to the more concentrated solution, we could effectively prevent osmosis, highlighting the invisible strength of osmotic pressure at work.