Question

A gas is allowed to expand in a well insulated container against a constant external pressure of $2.5\, atm$ from an initial volume of $2.50\, L$ to a final volume of $4.50\, L$. The change in internal energy $\Delta U$ of the gas in joules will be

• A. -500J
• B. -505J
• C. #ERROR!
• D. 1136.25J

Answer 1

Answer: (B)

-505J

Answer 2

$\Delta U = q + w$

For adiabatic process, $q=0$
$\therefore \Delta U = w$
$=- P \cdot \Delta V$
$=-2.5\, atm \times(4.5-2.5)\, L$
$=-2.5 \times 2\, L - atm$
$=-5 \times 101.3\, J$
$=-506.5\, J$
$\approx-505\, J$