The question is stated in the picture but I'll restate it:
A gas expands from I to F in the figure. The energy added to the gas by heat is 449 J when the gas goes from I to F along the diagonal path. What is the change in internal energy of the gas? Answer i units of J.
(delta)U=Q+W (In this case W is negative because the gas is doing work on the system)
The Attempt at a Solution
Since Q is given, I need to find W done by the gas.
Pressure is not constant, but its change is constant so I can use Paverage
Therefore W=(2*1.013*105)*2.5L=506,500 Joules
Inputting that into the equation for (delta)U:
449 J-506,500 J= -506,051 J
However this answer was incorrect. I also tried calculating work by finding the area under the graph IF, but this was wrong as well. I'm not really sure what I'm doing wrong. Could someone point me in the right direction?