A nonvolatile solute has no tendency to escape from solution into the vapor phase. XBP0B. A solution that has attraction or repulsion between components will have a negative or positive deviation from Raoult's law, respectively. Since the presence of a solute lowers the vapor pressure more heat energy is required for the liquid to change to a gas. When a solute is present in a solution it interruption the interactions required for freezing to occur. Osmotic Pressure A. A semipermeable membrane allows solvent but not solute molecules to pass through.
Osmotic pressure is the pressure needed to stop osmosis.