[anthony_ball]

I don't know what is the meaning of this term.

it can be calculated from this way.

e.g for the reaction N2O4---> 2 NO2

The observed relatve molecular mass of N2O4 =
(mole fraction of N2O4)*(its actual molecular mass) +  (mole fraction of NO2)*(its actual molecular mass)

i don't know why i can obtain it from this way..

THX!

[cliverlong]

Maybe (only maybe) because this is a reversible reaction that reaches a dynamic equilibrium there will be a mixture of both molecules, each with a "complementary" mole fraction, does the measured r.m.m. not equal either.


Clive

[Borek]

cliverlong is right - you can't separate NO₂ nor N₂O₄, you will alwyas have a mixture of both, so when you try to determine molar mass you will get a number reflecing both molar masses and their equilibrum ratio. To some extent that's similar to molar masses of elements - they are weighted averages of molar masses of isotopes.

[anthony_ball]

i can figure out it ... thx all