Heat added is not all converted to work
The mistake
Assuming an engine turns all input heat into useful work.
Why it feels right
Energy is conserved, so it seems it should all be usable.
How to catch it
Your efficiency came out at or above 100%.
The first principle
First law: ΔU = Q − W. The second law caps efficiency below 1 — some heat must be rejected to a cold reservoir.
worked mini-example
An engine absorbs 100 J. Can it do 100 J of work per cycle?
Common wrong move
Yes — energy is conserved.
Correct
No — it must exhaust some heat; efficiency < 100%.
Test the repair TH-02 · transfer
include J
Make a fresh prediction before referring to the worked example.