Why Am I Getting the Wrong Answer on My Molar Entropy Calculation?

[CzarValvador]

Working this thing on Web Assign. I feel like I've been doing everything 100% correct, yet I keep getting the wrong answer.

http://img510.imageshack.us/img510/4488/chemkp0.jpg

Basically, I need help on part B and C

What I did for B, I tried to calculate Delta S by using the equation n Cv ln(T2/T1)
I plugged in Cv given in the problem, used 341 for T2, and 298 for T1. n is One, since its for one mole. And I added the value I get to delta S to S that was given in the problem.

What have I been doing wrong.

 

[Bacat]

Maybe you should be plugging in $$C_p$$. The question says that the pressure is 1 atmosphere, even at the higher temperature. Therefore you must be operating at constant pressure and your volume must have increased.

 

[CzarValvador]

I've tried that multiple times. Thanks, though.