What happens when water vapour becomes a liquid?
When water vapor (gaseous water) condenses into liquid the molecules slow down due to a decrease in temperature. When the molecules lose sufficient kinetic energy, the attractive forces between the molecules become sufficient to allow the molecules to stick together. These attractive forces are called hydrogen bonds, and they are the electrostatic attractions between the partially negatively charged oxygen atoms in water and the partially positively charged hydrogen atoms. The amount of energy that steam must lose to condense into liquid water is 540 calories per gram.
