Preventing Gas Expansion: Molar Specific Heats at Constant Pressure & Volume

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SUMMARY

The discussion centers on the distinction between molar specific heats at constant pressure (Cp) and constant volume (Cv) in thermodynamics. It is established that work is associated with changes in volume, as expressed by the equation dW = PdV. Since work is performed during processes at constant pressure but not at constant volume, Cp and Cv are inherently different. The stationary force preventing gas expansion at constant volume does not perform work, reinforcing the difference between these two specific heats.

PREREQUISITES
  • Understanding of thermodynamic principles
  • Familiarity with the concepts of molar specific heat
  • Knowledge of work-energy relationships in physics
  • Basic grasp of pressure-volume relationships in gases
NEXT STEPS
  • Study the derivation of the relationship between Cp and Cv
  • Explore the implications of the first law of thermodynamics
  • Learn about the ideal gas law and its applications
  • Investigate real gas behavior and deviations from ideality
USEFUL FOR

Students and professionals in physics, engineering, and chemistry, particularly those focused on thermodynamics and gas behavior in various conditions.

chound
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Aren't we doing some work to prevent the gas from expanding if we maintain the constant volume. So shouldn't molar specific heat at constant pressure be equal to constant volume?
 
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You don't do work with a change in pressure, but rather a change in volume:

dW = PdV

Since work is done in the constant pressure case but not the constant volume one, Cp and Cv are different.
 
The force preventing the expansion is stationary. Only a moving force can do work.
 

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