# 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 :

$P =2.5\: atm$

$v_{i}=2.50L$

$v_{f}=4.50L$

$\Delta U=?$

Word done,

$W = -P \Delta v$

$=-2.5\left ( 4.50-2.50 \right )$

$=-5L-atm$

$=-5\times 101.3 J$

$=-506.5J$

$\therefore \Delta U=f+w$

$=-506.5J$

$=-505J$

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