What is Enthalpy of Vaporization ?

Ch3, Lesson E, Page 2 - What is Enthalpy of Vaporization ?

• Just to remind you, vaporization and boiling are the conversion of sat’d liquid into sat’d vapor.
• Boiling and vaporization require an energy input because at the same T and P sat’d vapor has a higher internal energy and a higher enthalpy than sat’d liquid.
• Condensation is the conversion of sat’t vapor into sat’d liquid.
• Condensation require that energy be removed from the system.
• The amount of energy that must be added to boil or vaporize a mole or kg of sat’d liquid is called the enthalpy or latent heat of vaporization.
• The heat of vaporization is also the amount of energy that must be removed when one mole of sat’d vapor condenses.
• The phrase “latent heat” just means that as this amount of energy is added, no temperature change occurs in the system.
• At a given pressure, a liquid boils at just one temperature and the system remains at that temperature as long as both phases are present.
• Therefore the energy input to boil a liquid is a “latent” heat.
• If you continue to transfer energy to the system after all the mass is sat’d vapor, the temperature of the system will begin to rise.
• This is called a sensible heat because it causes a change in temperature.