Worked Example
Understanding energy transfers as both heat and work is key to understanding the flows of energy that regulate Earth’s climate system. Describe how work is performed when a system expands against the force exerted by the atmosphere. In this case, has the system or the surroundings performed work?
When a system expands, the system exerts a force over a distance to push back the surrounding air. Therefore, the system performs work on the surroundings.
Your Turn
Describe the work performed when a system contracts.
When a system contracts, the surroundings must have exerted a force over a distance on the system. Therefore, in this case, the surroundings perform work on the system.