Reverse osmosis (RO) is a process used in chemistry and other fields to separate solvents from solute particles by applying external pressure to overcome the osmotic pressure gradient. It is a technique that utilizes a semipermeable membrane to selectively allow the passage of solvent molecules while rejecting solute particles.

Here are the key points about reverse osmosis:

1. Osmosis vs. Reverse Osmosis: Osmosis is the natural process by which solvent molecules move from an area of lower solute concentration to an area of higher solute concentration through a semipermeable membrane. Reverse osmosis, as the name implies, reverses this process by applying external pressure to force the solvent molecules to move from an area of higher solute concentration to an area of lower solute concentration.
2. Semipermeable Membrane: Reverse osmosis employs a semipermeable membrane that allows the passage of solvent molecules (typically water) while blocking the majority of solute particles, such as dissolved salts, minerals, and other contaminants. The membrane has tiny pores or channels that only permit the passage of small solvent molecules, effectively separating them from larger solute particles.
3. Pressure Application: To facilitate the reverse osmosis process, pressure is applied to the solution with a higher solute concentration, commonly referred to as the feed or influent stream. This pressure exceeds the osmotic pressure, which is the pressure required to prevent osmosis, and allows the solvent molecules to overcome the osmotic pressure and move through the membrane.
4. Solvent Purification: Reverse osmosis is widely used for water purification and desalination, as it effectively removes various dissolved impurities, including salts, minerals, organic compounds, and contaminants. The result is purified water with reduced levels of dissolved solids and improved quality.
5. Industrial Applications: Reverse osmosis has diverse applications in various industries, including water treatment, food and beverage processing, pharmaceutical production, chemical purification, and wastewater treatment. It provides an efficient and economical means of separating solvents from solutes, improving the quality and purity of the desired products.
6. Limitations: While reverse osmosis is effective in removing many solutes, it may not completely eliminate all dissolved substances. Some small molecules or ions can still pass through the membrane, and specific membranes may have different rejection capabilities for different solutes. Additionally, the process requires energy input due to the pressure needed to drive the solvent flow.

Reverse osmosis is a valuable technique for separating solvents from solutes and has wide-ranging applications in water treatment, purification, and other industries. It enables the production of purified water and the concentration or removal of solutes, contributing to various technological advancements and improving the quality of numerous products.