Adiabatic means no heat transfer, not constant temperature

01
The tempting model
Treating Q = 0 as if ΔT = 0.
02
Why it feels right
No heat added sounds like the gas temperature should not change.
03
Where it breaks · how to catch it
You set ΔU = 0 in an adiabatic compression or expansion.
04
The correct model
Adiabatic means Q = 0. The gas temperature can change because work changes internal energy: ΔU = Q − W_by.
05
Repair · see it, then test it
worked example A gas is compressed quickly in an insulated cylinder. What happens to temperature?
Tempting move
No change because Q = 0.
Correct move
It rises because work is done on the gas, increasing internal energy.
Test the repair TH-03 · transfer

An ideal gas expands adiabatically and does positive work. What happens to its internal energy?
It increases It decreases It stays constant because Q = 0 It must become zero

Make a fresh prediction before referring to the worked example.