Derive Entropy Change for Ideal Monatomic Gas

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Homework Help Overview

The discussion revolves around deriving the change in entropy for a monatomic ideal gas transitioning between two states characterized by pressure and volume. The original poster seeks to understand the correct expression for entropy change, which involves temperature and volume ratios.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • The original poster attempts to derive the entropy change expression but questions the validity of their result due to a missing unit of moles in their equation. Other participants inquire about the units involved and the exact problem statement to clarify the context.

Discussion Status

The discussion is ongoing, with some participants seeking clarification on the original poster's approach and assumptions. The original poster has indicated a resolution to their confusion regarding the assumptions made in a related derivation, but the overall consensus on the correct expression has not been reached.

Contextual Notes

There is mention of an assumption regarding the number of moles being equal to one in a prior derivation, which may have influenced the original poster's calculations. The need for clarity in the problem statement and the units of the variables involved is also highlighted.

SalfordPhysics
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A Monatomic gas passes from state 1 (pressure p1, volume V1) to state 2 (p2, V2).
Derive an expression for the change in entropy of a monatomic ideal gas.

The required final equation is: ΔS = Cv ln(T2/T1) + nRln(V2/V1)

In my attempt, I am retrieving ΔS = Cv ln(T2/T1) + Rln(V2/V1)
i.e.; the unit of moles not present in the "(V2/V1)" term.
Is the given form to obtain incorrect or am I making a very silly mistake to do with the prior assumptions?
 
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It is very difficult to help you if you do not state how you are arriving at your expression.

For the future, also leave the headings of the homework template in your post.
 
What are the units of Cv, R, and ΔS?

What is the exact statement of the problem?

Chet
 
Its not a problem now I figured things out, the problem was my solved form wasn't exactly as required, but like I thought I was making a mistake with a moles = 1 assumption in another derivation that i was using a a "subroutine".
 

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