A system performs mechanical work equal to 15 kJ and looses 2 kJ of heat to surrounding. What is the change…
A system performs mechanical work equal to 15 kJ and looses 2 kJ of heat to surrounding. What is the change in internal energy of a system?
-15 kJ
-17 kJ
13 kJ
19 kJ
Solution
$\mathrm{W}=-15 \mathrm{~kJ}, \mathrm{Q}=-2 \mathrm{~kJ}$ According to the first law of thermodynamics,
$\Delta \mathrm{U}=\mathrm{Q}+\mathrm{W}=-2+(-15)=-17 \mathrm{~kJ} .$