Achieve Week 3 and 4 Question 17

[Sophia_Venegas_3F]

I am having trouble with the second part of this question. I thought there was 0 work done so then q would be the same as delta U but achieve marked it wrong. Any help would be much appreciated! Here is the question:

A 0.721 mol sample of N2 (g) initially at 298 K and 1.00 atm, is held at constant pressure while enough heat is applied to raise the temperature of the gas by 20.1 K. Calculate the amount of heat q required to bring about this temperature change and find the corresponding total change in the internal energy delta U of the gas. Assume that the constant pressure molar specific heat for N2 (g), which consists of linear molecules, is equal to 7R/2, where R=8.1345 J/(mol*K) is the ideal gas constant.

Thanks!

[Chem_Mod]

If the gas is held at constant pressure while it is being heated, it must expand. You will have to calculate the volume expansion by using the ideal gas formula, PV = nRT, to find the initial and final volume of the gas. Because the system is at a constant pressure of 1 atm, you know it is expanding against an external force of 1 atm. Use the equation w = -PV to calculate the work done by the system against the surroundings.