Change in Entropy and adiabatic process

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SUMMARY

In an adiabatic and reversible process, such as compressing a gas in a tube, the change in entropy (dS) is zero. This conclusion is based on the principle that there is no heat flow (dQ=0) during the process, which maintains the system in equilibrium. Consequently, the equation dS = dQ/T confirms that entropy remains unchanged when the gas is compressed without heat exchange, despite the increase in temperature.

PREREQUISITES
  • Understanding of thermodynamic principles, specifically adiabatic processes
  • Familiarity with the concept of entropy and its mathematical representation (dS = dQ/T)
  • Knowledge of the behavior of gases under compression and temperature changes
  • Basic grasp of reversible processes in thermodynamics
NEXT STEPS
  • Study the laws of thermodynamics, focusing on the first and second laws
  • Explore the implications of adiabatic processes in real-world applications
  • Learn about the mathematical derivation of entropy changes in various thermodynamic processes
  • Investigate the differences between reversible and irreversible processes in thermodynamics
USEFUL FOR

This discussion is beneficial for students and professionals in physics, engineering, and thermodynamics, particularly those interested in understanding entropy and its behavior in adiabatic processes.

grscott_2000
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If a process is adiabatic and reversible, such as a gas in a tube that has been compressed, is it true to say that there is no change in entropy from the gas being uncompressed to being compressed?

If not, why not?
 
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grscott_2000 said:
If a process is adiabatic and reversible, such as a gas in a tube that has been compressed, is it true to say that there is no change in entropy from the gas being uncompressed to being compressed?

If not, why not?
Entropy is defined as heat flow / temperature at equilibrium: dS = dQ/T. If the process is adiabatic and reversible, this means there is no heat flow and at all times the system is in equilibrium. So dQ=0. So that pretty much means that dS = 0 (ie. no change in entropy).

AM
 
Last edited:
You can see that without taking into account the equation dS=dQ/T.
The entropy of the gas in a cylinder is increased when its temperature is increased and the entropy is decreased when its volume is reduced. When you compress the cylinder of gas without heat exchange, its volume is reduced while its tempereture raises, so entropy is unchanged. dS=0
 

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