Adiabatic means no heat transfer, not constant temperature
The mistake
Treating Q = 0 as if ΔT = 0.
Why it feels right
No heat added sounds like the gas temperature should not change.
How to catch it
You set ΔU = 0 in an adiabatic compression or expansion.
The first principle
Adiabatic means Q = 0. The gas temperature can change because work changes internal energy: ΔU = Q − W_by.
worked mini-example
A gas is compressed quickly in an insulated cylinder. What happens to temperature?
Common wrong move
No change because Q = 0.
Correct
It rises because work is done on the gas, increasing internal energy.
Test the repair TH-03 · transfer
Make a fresh prediction before referring to the worked example.