Entropy Change of an Ideal Gas

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SUMMARY

The discussion focuses on calculating the entropy change of an ideal gas during a quasi-static adiabatic expansion, specifically from state V1T1 to state V2T2. The key equation used is TVγ-1 = constant, which is crucial for demonstrating that the entropy change (dS) is zero in this process. Participants explore the relationship between temperature and volume, using the equation dS = dQr / T and the expression dS = Cv(dT/T) + R(dV/V) to analyze the problem. The consensus is that the approach to substitute temperature in terms of volume is valid, but further calculations are necessary to confirm the results.

PREREQUISITES
  • Understanding of thermodynamics, specifically the concepts of entropy and adiabatic processes.
  • Familiarity with the ideal gas law and its implications for temperature and volume relationships.
  • Knowledge of the specific heat capacities Cv and R for ideal gases.
  • Experience with calculus, particularly in applying differential equations to physical systems.
NEXT STEPS
  • Study the derivation of the entropy change formula for ideal gases in detail.
  • Learn about quasi-static processes and their significance in thermodynamics.
  • Explore the implications of the first and second laws of thermodynamics on entropy changes.
  • Investigate the role of specific heat capacities in various thermodynamic processes.
USEFUL FOR

Students and professionals in physics and engineering, particularly those studying thermodynamics, will benefit from this discussion. It is especially relevant for those tackling problems related to entropy changes in ideal gases.

mouzis
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Homework Statement


Using the expression for the entropy change of an ideal gas when the volume and temperature change and TV\gamma-1 = constant, show explicitly that the change in entropy is zero for a quasi-static adiabatic expansion from state V1T1 to state V2T2.

Homework Equations


TV\gamma-1 = constant

dS = dQr / T

The Attempt at a Solution



My idea was to use T1V1\gamma-1 = T2V2\gamma-1 and solve for T in terms of V and substitute into the second equation. I couldn't figure it out from there, so my question is is my idea of what to do fundamentally wrong, or is my calculation once i set up the problem wrong?
 
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$$dS=C_v\frac{dT}{T}+R\frac{dV}{V}$$
 

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