What is Latent Heat?

Latent Heat

    Latent heat is the name given to energy which is either lost or gained by a substance when it changes state, for example from gas to liquid. It is measured as an amount of energy, joules, rather than as a temperature.

     Most substances can exist in three states: gas, liquid and solid, though there is an additional state named plasma. The main difference between a substance in each state is how quickly its molecules are moving. As a liquid, the molecules move at a speed where they can repeatedly join together, break apart, then join together again. When they move slowly, they stay joined together, forming a solid. When they move quickly, they stay broken apart, forming a gas.

 Definition provided by Wisegeek

Important thing to know

  Why does the temperature not change when thermal energy is applied?

      1.  First, remember temperature is an expression of kinetic energy, so if  the kinetic energy isn't changing then were is the thermal energy going? 

      2.  If it's not going into kinetic energy, then the energy has to be dumped into potential energy.  

      3.  The "bonding" between molecules in solid and a liquid is from the attraction between a positive end of molecule to the negative end of another molecule

      4.  Using Coulomb's Law we can determine that the potential energy is negative.

      5.  The greater the negative amount of energy, the higher the stability of that matter

      6.  For solids the amount of negative potential energy higher then any of the other basic states of matter. 

      7. The thermal energy that is entering is reducing the amount of negative energy (making it less stable)


Important Equations

Q = m L

Q = Thermal energy (heat) 

m = mass 

L = Latent heat