IB DP Physics: SL复习笔记3.1.3 Internal Energy

Internal Energy

  • When a substance gains or loses thermal energy, its internal energy increases or decreases
  • The internal energy of a substance is defined as:

The sum of the total kinetic energy and the total intermolecular potential energy of the particles within the substance

  • As thermal energy is transferred to a substance, two things can happen:
    • An increase in the average kinetic energy of the molecules within the substance - i.e. the molecules vibrate and move at higher speeds
    • An increase in the potential energy of the molecules within the substance - i.e. the particles get further away from each other or move closer to each other

3-1-3-diagram-1---kinetic-energy-and-potential-energy

  • Since temperature is a measure of the average kinetic energy of the molecules, only an increase in the average kinetic energy of the molecules will result in an increase in temperature of the substance
    • Due to thermal expansion, when the temperature of a substance increases, the potential energy of the molecules also increases
  • When only the potential energy of the molecules changes, the temperature of the substance does not change
    • This is the case for all state changes (e.g. melting, boiling)

Exam Tip

Remember that a change in internal energy does not necessarily corresponds to a change in temperature.

  • A change in the average kinetic energy of the molecules corresponds to a  change in temperature
  • A change in the average potential energy of the molecules does not affect temperature

 

 

 

 

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