Question

A system absorbs $640J$ heat and does work of $260J$, the change in internal energy of the system will be:

• A. $+380J$
• B. $-380J$
• C. $+900J$
• D. $-900J$

Answer 1

The correct option is A $+380J$

The system absorbs $640J$ and the work system does on surroundings is $260J$. Therefore by the first law of thermodynamics, the internal energy of the system increases by:
$△U=q-W=(640-260)=+380J$.