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) -500 J
(b) -505 J
(c) +505 J
(d) 1136.25 J
(a) -500 J
(b) -505 J
(c) +505 J
(d) 1136.25 J