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

  • Thread starter Thread starter CzarValvador
  • Start date Start date
  • Tags Tags
    Chemistry Entropy
Click For Summary
SUMMARY

The discussion centers on the calculation of molar entropy using the equation ΔS = n Cv ln(T2/T1) for a system at constant pressure. The user initially used Cv for their calculations but was advised to use Cp instead, as the problem specifies constant pressure conditions at 1 atmosphere. The correct approach involves substituting Cv with Cp and ensuring that the volume change is accounted for during the calculation. The user is encouraged to verify their values for T2 and T1, which are 341 K and 298 K respectively, to ensure accuracy in their entropy calculation.

PREREQUISITES
  • Understanding of thermodynamic concepts, specifically molar entropy.
  • Familiarity with the equations for entropy change, particularly ΔS = n Cp ln(T2/T1).
  • Knowledge of the difference between constant volume (Cv) and constant pressure (Cp) heat capacities.
  • Basic skills in manipulating logarithmic functions and temperature conversions.
NEXT STEPS
  • Review the principles of thermodynamics focusing on entropy calculations.
  • Study the differences between Cv and Cp, including when to use each in calculations.
  • Practice problems involving molar entropy at constant pressure using real gas scenarios.
  • Explore the implications of temperature changes on entropy in thermodynamic systems.
USEFUL FOR

Chemistry students, educators, and professionals involved in thermodynamics and physical chemistry who seek to enhance their understanding of entropy calculations and related concepts.

CzarValvador
Messages
5
Reaction score
0
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.
 
Last edited by a moderator:
Physics news on Phys.org
Maybe you should be plugging in [tex]C_p[/tex]. 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.
 

Similar threads

Chemistry Two approaches to calculating entropy differ by factor of two. Why?
  • · Replies 3 ·
Replies
3
Views
3K
Chemistry A calculation of enthalpy, entropy, and Gibbs energy of vaporization
  • · Replies 1 ·
Replies
1
Views
2K
Chemistry Where Did I Go Wrong in My Gas Law Calculation?
  • · Replies 2 ·
Replies
2
Views
3K
Chemistry How do we use enthalpy of formation in this calculation?
  • · Replies 9 ·
Replies
9
Views
3K
Chemistry Understanding the calculation of enthalpy of the formation of benzene
  • · Replies 3 ·
Replies
3
Views
3K
How do I find the entropy variation?
  • · Replies 6 ·
Replies
6
Views
3K
Chemistry Finding the molecular formula of an unknown hydrocarbon
  • · Replies 4 ·
Replies
4
Views
3K
Why Is Cv Used in This Example?
  • · Replies 1 ·
Replies
1
Views
2K
Change in Entropy When Mixing Water at Different Temperatures
  • · Replies 5 ·
Replies
5
Views
2K
I am stuck on a calculation -- Entropy change for a compound system
  • · Replies 10 ·
Replies
10
Views
2K