Chapter 6: Unit 9. Vapor Pressure

Vapor Pressure

When a liquid is placed in an open container, liquid molecules near the surface that have enough kinetic energy to overcome the intermolecular forces escape to the gas phase. This process is called evaporation and it is an endothermic process. The opposite process is called condensation which is an endothermic process, where gas molecules lose energy and go back to the liquid phase.  Vapor pressure is the pressure of the gas molecules above a liquid in equilibrium in a closed container. The vapor pressure increases with increasing temperature. When the vapor pressure of the gas molecules is equal to the external pressure ( 1 atm). The liquid boils.

liquid boiling