Question

A system absorbs $20kJ$ heat and also does $10kJ$ of work. The net internal energy of the system:

• A. Increases by $10kJ$
• B. Decreases by $10kJ$
• C. Increases by $30kJ$
• D. Decreases by $30kJ$

Answer 1

The correct option is A Increases by $10kJ$

According to the first law of thermodynamics,
$\Delta U=q+W$
Where, $\Delta U$ = change in internal energy.
Since,
The heat absorbed by the system is $q=20kJ$
The work done by the system is $W=-10kJ$

$\therefore ,\Delta U=20-10kJ=10kJ$

So, the net internal energy of the system increases by $10kJ$