Latent Heat & Change of State Adding or removing heat does not always result in a change of temperature. During a change of state, the heat added is called latent heat because there is no change in temperature. Latent means "hidden". Notice in the graph above that while ice is melting (change of state) the temperature stays constant at 0°C. The temperature also is constant when water boils and changes to steam or vapour. When a solid is melting the heat energy added is building up the potential energy of the molecules to break the electrical forces holding them together. Similarly, when liquids are turning to gases the heat energy increases the energy of the molecules so they get further apart and become gas molecules. Latent heat of fusion is the amount of heat required to melt 1 kg of a substance without changing its temperature. The latent heat of fusion for water is 3.3 x 105 J/kg, which means that 3.3 x 105 J of energy are needed to change 1 kg of ice at 0°C into water at 0°C. Latent heat of vaporization is the amount of heat required to vaporize 1 kg of a substance without changing its temperature. Latent Heat Formula Latent heat can be calculated using the following formula:

How do steam boilers work?

http://www.youtube.com/watch?v=a0xZPl_bwHI&feature=player_embedded