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Key Idea 2
Describing Energy Transfers
Concept Question: How do scientists describe energy flow to or from a system?

Question for Thought

Suppose it is a hot day and your air conditioner is broken. Could you cool your home by opening the door of your refrigerator?

 A refrigerator

To answer this question, we need to carefully keep track of the different energy transfers that occur within a refrigerator. Scientists keep track of energy transfers between objects by focusing on a particular object or set of objects, called the system, and distinguishing it from the surroundings. However, the system and surroundings must be chosen very carefully, because the choice you make will affect how the transfer of energy is described.

Your Turn!

Carefully defining the system is an important step when describing the energy transfers that occur in Earth’s climate or when analyzing the energy conversions in a refrigerator. When describing the energy transfers in a refrigerator, what do you think should be defined as the system?

Click here to show answer
At first glance, it may seem reasonable to define the system as the entire refrigerator. However, only one part of the refrigerator is actually responsible for the energy transfers that occur: the refrigerant fluid. Therefore, we will define our system as the refrigerant fluid. Every other part of the refrigerator and all the surrounding air are part of the surroundings.