Calculating Maximum Work from Cooling Liquid Reversibly

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SUMMARY

The discussion focuses on calculating the maximum work that can be done by cooling a liquid reversibly. The liquid has a constant molar heat capacity of 132 J/mol K and is initially at 80°C, cooling to 25°C. The total heat released during this process is 7260 J, but the maximum work calculated is 601 J. This discrepancy arises from the relationship between internal energy change and work done, as defined by the first law of thermodynamics, ΔU = Q - W.

PREREQUISITES
  • Understanding of thermodynamic principles, specifically the first law of thermodynamics.
  • Knowledge of heat capacity concepts, including constant molar heat capacity.
  • Familiarity with reversible processes in thermodynamics.
  • Ability to calculate changes in entropy and internal energy.
NEXT STEPS
  • Study the derivation of the first law of thermodynamics and its applications.
  • Learn about the concept of reversible processes and their significance in thermodynamics.
  • Explore the relationship between heat transfer and work done in thermodynamic systems.
  • Investigate the calculation of maximum work in various thermodynamic scenarios.
USEFUL FOR

This discussion is beneficial for students in thermodynamics, particularly those studying heat transfer and energy calculations, as well as professionals in engineering and physical sciences who require a deeper understanding of reversible processes and work calculations.

phizzle86
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Homework Statement



One mole of a liquid with a constant molar heat capacity of 132 j/mol K is initially at a temp of 80 C. The heat capacity is independent of tempearture. Calculate the maximum work that could have been done onthe surroundings while cooling the liquid reversibly. The surroundings are at a temp of 25 C.


Homework Equations



Given: q= -7260 J , change in entropy= 22.3J/K for the cooling

Change entropy = (Cvdt)/T



The Attempt at a Solution



I guess my problem here is not understanding what maximum work is, i would think that the maximum work here is in a reversible process would be the total amount of heat that is released that has the potential to do work, so wouldnt' that b 7260 J? The answer provided is 601 J

thanks guys
 
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I'm not sure this is helpful because I don't see how the answer of 601 J was arrived at, but from first law ΔU=Q-W where ΔU=n∫Cv*dt. For a liquid Cv≈Cp but Cp is constant therefore ΔU=n*Cp*ΔT. Maximum work would occur if Q=0 (insulated container). Therefore Wmax=ΔU

Maybe I am missing something
 

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