internal energy

• Internal energy


  The energy stored in a system by the particles, which includes the total kinetic energy and potential energy of all the atoms and molecules that make up the system
• Melting


  Solid turns into a liquid as internal energy is increased
• Boiling


  Liquid turns into a gas as internal energy is further increased
• Condensation


  Gas turns back into a liquid as internal energy is decreased
• Freezing


  Liquid turns into a solid as internal energy is decreased further
• Sublimation


  A solid can turn directly into a gas, without going through the liquid state
• Mass is always conserved during changes of state
• Physical changes are reversible, and the material recovers its original properties
• Evaporation


  A liquid tends to turn into a gas, but only on the surface of the liquid
• Particles on the surface of a liquid have enough energy to turn into a gas during evaporation