For each of the following adiabatic processes, find the change in internal energy. ( $a$ ) A gas does $5 \mathrm{~J}$ of work while expanding adiabatically. (b) During an adiabatic compression, $80 \mathrm{~J}$ of work is done on a gas.
During an adiabatic process, no heat is transferred to or from the system.
(a) $\Delta U=\Delta Q-\Delta W=0-5 \mathrm{~J}=-5 \mathrm{~J}$
(b) $\Delta U=\Delta Q-\Delta W=0-(-80 \mathrm{~J})=+80 \mathrm{~J}$