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 ∆U of the gas in joules will be:

• A. 1136.25 J
• B. −500 J
• C. −505 J
• D. +505 J