The examples on the last page show that how you define your system is very important and will affect the conclusions you make concerning the energy transfers between a system and the surroundings. While there is no right or wrong way to define the system, your definition will depend on the questions you are trying to answer. Answer the following questions to practice defining a system that will allow you to address a specific problem.

Worked Example

The food in your refrigerator is constantly too warm, so you want to figure out how much thermal energy is being removed from the inside of your refrigerator. To describe the energy transfer, what should the system be? After defining your system, describe the direction of energy transfer.

Your Turn

You have learned that your refrigerator releases thermal energy, so you now want to know how much the temperature in your kitchen increases because of this. In this situation, how should you define your system? Then, describe the direction of energy transfer.