Question

A gas does $4.5J$ of external work during adiabatic expansion. If its temperature falls by $2K$, then its internal energy will be:

• A. increased by $4.5J$
• B. decreased by $4.5J$
• C. decreased by $2.25J$
• D. increased by $9.0J$

Answer 1

The correct option is B decreased by $4.5J$

Since it is an adiabatic expansion: $dQ=0$

$\Rightarrow dU=-dW$

$\Rightarrow dU=-4.5J$