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## Homework Statement

calculate the change of entropy (for the system) when 3 moles of a monatomic perfect gas, for which Cp,m = (5/2) R, is heated and compressed from 298K and 1atm to 398K and 5atm.

ans: -22.1 JK-1

## Homework Equations

for an ideal gas, Pv=nRT

for iso-choric condition, delta S = Cv ln(T2/T1)

## The Attempt at a Solution

as both the P and T increase, by Pv=nRT v should be constant at this case

so i thought i should use Cv ln(T2/T1)

however the model answer is that it uses nCp,m ln(T2/T1) + nRln(V2/V1)

i don't know which part of my concept is wrong...

pls help, thank you!