What effect does adding more solute have on the vapor pressure of a solution?

Adding more solute to a solution decreases the vapor pressure compared to that of the pure solvent due to a phenomenon known as Raoult's Law. This law states that the vapor pressure of a solvent in a solution is directly proportional to the mole fraction of the solvent present. When additional solute is introduced, the concentration of the solvent molecules relative to the solute molecules decreases, leading to fewer solvent molecules escaping into the vapor phase.

The presence of solute particles disrupts the surface of the solvent, reducing the ability of solvent molecules to evaporate. As a result, the vapor pressure of the solution is lower than that of the pure solvent. This is a key principle in understanding colligative properties, where the presence of solute affects the physical properties of the solvent, including freezing point depression, boiling point elevation, and vapor pressure lowering.