Is Total Molar Concentration Constant in an Isothermal System?

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SUMMARY

Total molar concentration remains constant in an isobaric isothermal system due to the equilibrium established between solid naphthalene and its vapor. The perfect gas equation (PV=nRT) indicates that while pressure (P) and temperature (T) are constant, the volume (V) can change, leading to variations in the number of moles (n). However, as n changes, total molar concentration remains constant at a value of 1, as the system adjusts to maintain equilibrium. The relationship C=CA+CB holds true under these conditions, confirming the constancy of total molar concentration.

PREREQUISITES
  • Understanding of the perfect gas equation (PV=nRT)
  • Knowledge of phase equilibrium concepts, particularly involving solids and vapors
  • Familiarity with isothermal and isobaric processes
  • Basic principles of molar concentration and its calculation
NEXT STEPS
  • Study the implications of the perfect gas law in varying conditions
  • Explore phase equilibrium dynamics, particularly in solid-vapor systems
  • Learn about the mathematical derivation of molar concentration in different states
  • Investigate the behavior of gases in isothermal and isobaric processes
USEFUL FOR

Chemistry students, chemical engineers, and professionals involved in thermodynamics and phase equilibrium analysis will benefit from this discussion.

mech-eng
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how can we understand total molar concentration remains constant in a isobaric isothermal system? if it is from perfect gas equation pv=nrt although p and t are constant but v isn't constant so since mol number can be change over volume, total molar concentration may change.it is a situation of a tube with one end is surrounded by gaseous nitrogen and one end is closed with a solid naphthalene in equilibrium with its vapor.
 
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Total molar concentration remains constant because n can change
probably: if it is solid napthalene in equilibrium with its vapor, then napthalene atoms can desorb and enter the gas phase to maintain equilibrium. so if volume changes, n will change correspondingly
 
But it must always be constant which is equal to 1 so we shouldn't limit the situation to the isobaric isothermal case.Am I right? is C=CA+CB always true or only for at constant
T and P
 
Last edited:

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