# Mole fractions

1. Oct 11, 2006

### asdf1

Does X=n? X is the element fraction in a compound, and n is the mole number of an element.

2. Oct 11, 2006

### Astronuc

Staff Emeritus
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.

3. Oct 11, 2006

### asdf1

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
4. Oct 11, 2006

### Astronuc

Staff Emeritus
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

5. Oct 12, 2006

thank you~