Internal Energy

• Energy is stored inside a system by the particles (atoms and molecules) that make up the system ; this is called internal energy
• Internal energy is the total kinetic energy and potential energy of all the particles (atoms and molecules) that make up a system
• Heating changes the energy stored within the system by increasing the energy of the particles that make up the system. This either raises the temperature of the system or produces a change of state
• A change in state occurs the particles have enough energy in their kinetic energy stores to break the bonds holding them together
• The specific heat capacity of a substance is the amount of energy required to raise the temperature of one kilogram of the substance by one degree celsius
• ∆ E = m c ∆ θ

  • Change in thermal energy (∆E) in joules (J)
  • Mass (m) in kilograms (kg)
  • Specific heat capacity (c) in joules per kilogram per degree Celsius (J/kg °C)
  • Temperature change (∆θ) in degrees Celsius (°C)
• The energy needed for a substance to change state is called latent heat. When a change of state occurs, the energy supplied changes the energy stored (internal energy) but not the temperature
• The specific latent heat of a substance is the amount of energy required to change the state of one kilogram of the substance with no change in temperature
• $energy \; for \; a \; change \; in \; state =$$mass \times specific \; latent \;heat$

  $E=$$mL$

  • Energy (E) in joules (J)
  • Mass (m) in kilograms (kg)
  • Specific latent heat (L) in joules per kilogram (J/kg)
• Specific latent heat of fusion 


  Change of state from solid to liquid
• Specific latent heat of vaporisation

  Change of state from liquid to vapour
• When the substance is melting or boiling the internal energy increases and that energy is used to break bonds between particles 


  Heating graphs

  
• When the substance is condensing or freezing bonds are forming between particles which releases energy so the internal energy decreases while the temperature does not 


  Cooling graph