Question

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

• A. $+505J$
• B. $+1136.25J$
• C. $-500J$
• D. $-505J$

Answer 1

The correct option is D $-505J$

The change in the internal energy is given by the following expression.
$\Delta U=q+W$
Since container is well insulated, $q=0$.
Hence, $\Delta U=W=-P\Delta V$
$\Delta U=W=-2.5atm\times (4.50L-2.50L)$
$\Delta U=W=-5.0Latm$
Convert the unit to J
$\Delta U=W=-5.0Latm\times \frac{101.33J}{1Latm}=-505J$