internal energy

• Particles in a solid

  • Do not move but vibrate
• Particles in a liquid

  • Can move around each other
• Particles in a gas

  • Move extremely rapid
• All of these particles have kinetic energy
• Particles also have potential energy (intermolecular forces and chemical bonds)
• Internal energy


  The energy stored in a system by the particles. Internal energy is the total kinetic energy and potential energy of all the particles (atoms and molecules) that make up a system
• Heating a solid


  1. Increases the internal energy

  2. Solid turns into a liquid by melting

  3. Heating the liquid further increases the internal energy

  4. Liquid turns into a gas by boiling
• Cooling a gas


  1. Reduces the internal energy

  2. Gas turns back into a liquid by condensation

  3. Cooling the liquid further reduces the internal energy

  4. Liquid turns to a solid by freezing
• Sublimation


  When a solid can turn directly into a gas
• When changes of state take place mass is always conserved. We are not adding or taking away any particles.
• Changes of state are physical changes not chemical changes. If we reverse the change the material recovers its original properties.
• Evaporation


  When a liquid turns to a gas but only on the surface of a liquid. In this case only the particles on the surface have enough energy to turn into a gas