The first law of thermodynamics is a statement of:

1. First law: ΔU = Q − W, where Q is heat added to system and W is work done BY system. 2. It says the change in internal energy of a system equals the net energy transferred to it. 3. So it is simply the principle of energy conservation extended to include heat. _Source: syllabus Physics Ch 11 "Thermodynamics", §11.5 First Law_