Thermal Equilibrium (Cambridge (CIE) A Level Physics)

Defining thermal equilibrium

• Regions in thermal equilibrium have equal temperature

• Thermal equilibrium occurs when there is no longer thermal energy transfer between regions

• Thermal equilibrium between two substances in physical contact is defined as:

  When there is no longer an exchange of any heat energy and both regions reach an equal temperature

Illustrating thermal equilibrium

Two regions of different temperatures reach thermal equilibrium after some time

• The hotter region will cool down and the cooler region will heat up until they reach thermal equilibrium

• The final temperature of a system depends on the initial temperature difference between the two regions

• For example: ice cubes placed in a glass of room-temperature water

  • The ice cubes heat up as energy is transferred from the water

  • The water cools down, due to the energy transferred away, until they both reach the same temperature

  • Thermal equilibrium is achieved when the ice has melted and the water reaches a temperature somewhere between the initial temperatures of the ice and room-temperature water