Required heat, entropy change of object dropped in water

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Homework Help Overview

The problem involves a gas (argon) in a container, initially at a specific pressure and temperature, being dropped into a pool of water at a higher temperature. The discussion focuses on calculating the heat required to raise the gas temperature and the associated entropy changes for the gas and the universe, while ignoring the container's entropy change.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the calculation of entropy changes for both the gas and the universe, questioning the need for the number of moles in these calculations. There is an exploration of the relationship between heat added and entropy change, particularly in the context of constant volume and temperature changes.

Discussion Status

Some participants have provided guidance on the necessity of including the number of moles in entropy calculations. There is an acknowledgment of the initial calculations and a recognition of the need for further clarification on certain aspects of the problem.

Contextual Notes

Participants note the initial pressure and volume of the gas as important factors in the calculations, indicating potential constraints or assumptions that may affect the analysis.

ElectricEel1
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Homework Statement


A 1 liter container is filled with argon to pressure of 10^5Pa at 303K. Dropped into pool at temp 323K. How much heat is needed to heat the gas to 323K? what is the entropy change in the gas and the universe? ignore the entropy change in container.

Homework Equations


c_v=3/2*R
dq=cdt
deltaS=integral of dQ/T

The Attempt at a Solution


I started with the entropy:

reservoir:
T is constant so delta Q/ T_R = C(T_s-T_r)/T_r = 0.77. negative sign because its entropy reduced.
system:
evaluating the same integral with a non constant T gave me C*ln(T_r/T_s) = 0.79.
Universe:
change in the universes entropy was 0.02 after adding both of these together.

I'm unsure of these answers and at first I figured I should just use C(T_s-T_r) to find the heat added but the question mentions the initial pressure and the constant volume of 1 litre so I think I am missing something.
Thanks
 
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I figured I needed to find n so I calculated n to be 0.04 from pV=nRT.
Does this mean I should have had n before C in the entropy parts too?
 
ElectricEel1 said:
I figured I needed to find n so I calculated n to be 0.04 from pV=nRT.
Does this mean I should have had n before C in the entropy parts too?
Yes. You've done great.
 
Chestermiller said:
Yes. You've done great.
thank you sir
 

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