Examples of Vapor Pressure Lowering

When you place a glass of water in an open room, it will evaporate completely, however, if a cover is placed above the glass, the space above the liquid will gradually contain a constant amount of water vapor. Also, in some steam engines the cylinder can be cooled to lower the vapor pressure of the steam and create a suction on the back side of the piston to get extra power. By dissolving a solute in a liquid solvent, the vapor pressure of the liquid will come down. This happens because some liquid molecules will need to attach to the solute and therefore there are fewer liquid molecules to vaporize.