Practice question · Sort into groups
Sort each sign convention by what it represents for the system.
Groups: Energy entering the system · Energy leaving the system
- q is positive
- The system releases heat to the surroundings
- w is positive
- The gas expands against an external pressure
Hints
- Positive always means energy crossing INTO the system.
- An expanding gas pushes on its surroundings and spends energy doing so.
Show the answer
Energy entering the system: q is positive, w is positive
Energy leaving the system: The gas expands against an external pressure, The system releases heat to the surroundings
Why
The convention is uniform: positive and positive both mean energy entering. Expansion and heat release are the system paying energy out, so both carry negative signs.
Practise The First Law of Thermodynamics
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