How can we measure entropy using experiments.

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SUMMARY

This discussion focuses on measuring entropy through experimental methods, specifically referencing the equation ∫dQ/T for calculating entropy change. It critiques the Claussius entropy as being too phenomenological for direct observation and finds the Boltzmann definition unsuitable for experiments. The conversation also highlights the challenges of determining the entropy of a system, such as a tank of CO2, and suggests utilizing quasi-static processes from perfect crystals to calculate entropy changes, although this method is deemed economically impractical. A recommended resource for further understanding is the book "Thermodynamics for the Unsatisfied" by Thess, particularly page 85, which discusses the determination of entropy in simple systems.

PREREQUISITES
  • Understanding of thermodynamic principles, specifically entropy.
  • Familiarity with the Clausius and Boltzmann definitions of entropy.
  • Knowledge of quasi-static processes in thermodynamics.
  • Basic calculus for interpreting the integral ∫dQ/T.
NEXT STEPS
  • Read "Thermodynamics for the Unsatisfied" by Thess, focusing on entropy determination.
  • Explore the application of quasi-static processes in thermodynamic calculations.
  • Investigate experimental methods for measuring temperature and specific heat.
  • Study the implications of the second law of thermodynamics on entropy measurement.
USEFUL FOR

Students and professionals in physics, particularly those specializing in thermodynamics, as well as researchers interested in experimental methods for measuring entropy.

raopeng
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A friend asks me this. If considering the equation: ∫\frac{dQ}{T}, then it is technically feasible to work out some forms of expressions with measurable physical quantities like temperature and specific heat, therefore it is possible to work out a precise value for entropy change. But is there a more economic way? I think Claussius entropy is too phenomenological to be directly observed in experiments, and the Boltzmann definition is not suitable for experiments.

While above is about the entropy change, my friend also asks how to determine the entropy of a system, for example a tank of CO2. If a perfect crystal has zero entropy, does that meran in order to calculate the entropy we have to construct possible quasi-static processes from perfect crystals to the present compound and work out the entropy change, which seems to be very uneconomic?
 
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There is a good description in a book by Thess - search for "Thermodynamics for the unsatisfied" at amazon.com, and check "search inside this book". In the table of contents, click on page 85, "determination of the entropy of simple systems".
 
Thank you so much, this is really helpful.
 

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