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

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The user is struggling with molar entropy calculations on Web Assign, specifically parts B and C. They initially used the equation Delta S = n Cv ln(T2/T1) with the correct values but are still receiving incorrect answers. A suggestion was made to use C_p instead of C_v, as the problem specifies constant pressure conditions at 1 atmosphere. The user has attempted this approach multiple times without success. Clarification on the correct method for calculating entropy under these conditions is needed.
CzarValvador
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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.
 
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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.
 
I've tried that multiple times. Thanks, though.
 
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