Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Mole fractions

  1. Oct 11, 2006 #1
    Does X=n? X is the element fraction in a compound, and n is the mole number of an element.
     
  2. jcsd
  3. Oct 11, 2006 #2

    Astronuc

    User Avatar
    Staff Emeritus
    Science Advisor

    It may or may not depending on the basis.

    The mole number is usually given as a 'whole number' or 'integer', e.g. Al2O3 or C2H4.

    Mass fractions and mole fractions are different.

    Please provide an example.
     
  4. Oct 11, 2006 #3
    Ex. For a binary solution, there's a graph with the Gibbs free energy of componet A on the left y axis, Gibbs free energy of componet B on the right y axis, and with XB as the x axis.

    See the bottom diagram on pg6 of http://addis.caltech.edu/research/gibbs.pdf#search=%22gibbs%20free%20energy%20in%20binary%20solution%22 [Broken]

    the straight line that passes through point (4) and (5) also equals the chemical potential on intersecting the left and right y axes. Therefore, I'm wondering if dn=dx, because the definition for
    chemical potential=(dG)/(dn)
     
    Last edited by a moderator: May 2, 2017
  5. Oct 11, 2006 #4

    Astronuc

    User Avatar
    Staff Emeritus
    Science Advisor

    Xi = mole fraction of i = Ni / ΣNi

    x is written in terms of the mole fraction of one of the components,

    and

    If the (molar) gibbs free energy of pure A is gA, and that of pure B is gB, then the (molar) gibbs free energy for the combination of pure components is g (pure, combined) = gA•XA + gB•XB
     
  6. Oct 12, 2006 #5
    thank you~
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook