Practice question · Sort into groups
For each process on an ideal gas, sort by what the first law says about it. ( = heat added, = work done by the gas.)
Groups: Q = 0 · ΔU = 0 · W = 0
- Isothermal compression (constant T)
- Any cycle that returns the gas to its starting state
- Adiabatic expansion (insulated)
- Heating at fixed volume
Hints
- For an ideal gas, depends only on temperature: so constant pins to zero. And is a state function: back to the same state, back to the same .
- Gas does work only when it pushes a boundary through a distance: fixed volume means no work.
Show the answer
Q = 0: Adiabatic expansion (insulated)
ΔU = 0: Isothermal compression (constant T), Any cycle that returns the gas to its starting state
W = 0: Heating at fixed volume
Why
Each named process zeroes one term of , which is exactly what makes it solvable. Spotting the zero is always step one of a thermodynamics problem.
Practise First Law of Thermodynamics
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