Latent Heat
We like to impress upon students that water has a high specific latent heat of fusion (334 kJ/kg), and even higher specific latent heat of vaporization (2.260 MJ/kg). That’s why it feels so cold when we get out of the swimming pool. The amount of water on our wet skin may be small, but they sure used a lot of our body heat to evaporate away. It’s also why it feels so hot just before it rains. Those rain clouds are formed by condensing water vapour dumping huge amounts of latent heat into the atmosphere in the process.
Latent heat can be used to move a lot of thermal energy in a short time. In air conditioners, the coolant is made to vaporize and condense repetitively to move heat in or out of the room. It is amazing such a small amount of coolant can move so much heat.
Unlike melting, vaporization usually involves a large change in volume. This is why volatile liquids can make very fascinating toys. Check out the hand boiler and the drinking bird!
xmPhysics 