Question

How do you calculate the boiling point of a substance?

Answer 1

Normally, these are determined empirically – by experiment. They can be approximately calculated from correlations (Nomographs) and comparisons.

Explanation:

Most “calculations” are only based on pressure variations over a liquid with a known “normal” boiling point. Calculations of boiling point elevations due to solutes can be done easily once the fundamental factor for each solvent is known.

And example of a nomograph is here: http://www.sigmaaldrich.com/chemistry/solvents/learning-center/nomograph.html

The Clausius-Clapeyron Equation, which assumes the heat of vaporization is a constant over a pressure range, and Antoine´s Equation can be used, but also depend on previous empirical data.

Even with supercomputers the calculations and understanding of the atomic interactions make it very difficult “calculate” chemical properties without empirical reference points.

For example: http://www.hitachi.com/rev/pdf/2014/r2014_09_108.pdf
“First-principles Materials-simulation Technology” paper.