[Northstar]

Hi all,
I just finished my Chem homework but I'm not positive it's correct. The first question is: A balloon filled with an ideal gas has a volume of 45.5L. After the addition of 15.5kJ of heat, the internal energy increases by 11kJ. What is the final volume of the balloon, assuming that the external pressure is 1atm.

I used delta E = q + w to solve for work, then used w = - Pext delta V to find the final volume. I got 89.4L as my answer.

Second question is: 2.0 moles of an ideal gas are contained in a cylinder with a constant external pressure of 1.0 atm and at a temperature of 398K by a movable, frictionless piston. This system is cooled to 298K.
a) Calculate w (in kJ)
I used PV = nRT to find the initial and final volumes. Then I used w = -Pext delta V to find work. I got 1.66kJ
b) Given that 4.16kJ of heat are given off by the system, calculate the internal energy change for this ideal system.
I used delta E = q + w
delta E = -4.16kJ + 1.66kJ = -2.50 kJ