I have two physical chemistry textbooks, one by Atkins and one by Levine, which seem to differ in their notation used when describing Raoult's law.

Atkins talks about the molar fraction term in Raoult's law as if it were of the entire system.

Levine says that Raoult's law has the form $P_i = x^l_i P_i^\circ$, which seems to imply that $x^l_i$ is the molar fraction in the liquid.

So what is it really? And why would Levine use that notation?

Levine also uses this notation for Henry's law.


  • $\begingroup$ this is the definition as I was taught: $\frac{p_i}{p_{0i}}=x_i=\frac{n_i}{n}$ $\endgroup$ Apr 16, 2015 at 14:42
  • $\begingroup$ Can you let me know the exact things quoted in either of the books? It should be the fraction in liquid that matters. $\endgroup$ May 31, 2015 at 8:12
  • 1
    $\begingroup$ @SatwikPasani I think I've solved this now. As you say, its the fraction in the liquid. My main source of confusion I think came from the wording in most problems. Problems said "A mixture with $X_a$ and $X_b$... find the pressure in the vapor due to $a$", and that confused me because it doesn't specifically say that is the liquid phase they're talking about. Thanks for your help. $\endgroup$
    – DLV
    May 31, 2015 at 18:57


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