Chemistry Calculating X: Element Fraction from Mole Number

[asdf1]

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

 

[Astronuc]

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.

 

[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

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)

 

[Astronuc]

X_i = mole fraction of i = N_i / ΣN_i

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 g_A, and that of pure B is g_B, then the (molar) gibbs free energy for the combination of pure components is g (pure, combined) = g_A•X_A + g_B•X_B

 

[asdf1]

thank you~