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

1. A
   $-500\text{J}$
2. B
   $-505\text{J}$
3. C
   $+505\text{J}$
4. D
   $1136.25\text{J}$