Defining Thermal Equilibrium
- Thermal energy is always transferred from a hotter region to a lower region
- Thermal equilibrium is defined as:
When two substances in physical contact with each other no longer exchange any heat energy and both reach an equal temperature
- There is no longer thermal energy transfer between the regions
Illustrating Thermal Equilibrium
Two regions of different temperatures reach thermal equilibrium after some time
- The two regions need to be in thermal contact for this to occur
- 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
- Example: consider placing ice cubes in a glass of room-temperature water
- The ice cubes heat up as energy is transferred from the water
- The water cools down until they both reach the same temperature
- Thermal equilibrium will be achieved when the ice has melted and the water reaches a temperature somewhere between the initial temperatures of the ice and room-temperature water
