• Energy can be classified into two forms: kinetic or potential energy
• The molecules of all substances contain both kinetic and potential energies
  • Kinetic energy is due to the speed of the molecules
  • Potential energy is due to the separation between the molecules

   

• The amount of kinetic and potential energy a substance contains depends on its phase of matter (solid, liquid or gas)
  • This is known as the?internal energy

   

• The internal energy of a substance is defined as:

The sum of the randomly distributed kinetic and potential energies of the particles in a body

• The symbol for internal energy is?U, with units of?Joules?(J)
• Particles are randomly distributed, meaning they all have different speeds and separations
• The internal energy of a system is determined by:
  • Temperature?(higher temperature, higher kinetic energy and vice versa)
  • The?random motion?of molecules
  • The?phase of matter: gases have the highest internal energy, solids have the lowest
  • Intermolecular forces?between the particles (greater intermolecular forces, higher potential energy and vice versa) - this is linked to the phase (solid, liquid, gas) that the matter is in

   

• The internal energy of a system can increase by:
  • Doing work?on it
  • Adding heat?to it

   

• The internal energy of a system can decrease by:
  • Losing heat?to its surroundings
  • Changing state?from a solid to a liquid or liquid to a gas