# Isobaric isothermal system

1. ### mech-eng

211
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.

2. ### Hyo X

61
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

3. ### mech-eng

211
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: Oct 31, 2013