Guldberg's rule

The Guldberg rule states that the normal boiling point of a substance is around two thirds of the critical temperature : ${\displaystyle T_{\mathrm {s} }}$ ${\displaystyle T_{\mathrm {k} }}$

${\displaystyle T_{\mathrm {s} }\approx {\frac {2}{3}}\,T_{\mathrm {k} }}$

This rule is a rough approximation of the actual relationship. The constant , usually designated with Θ, is substance-specific and takes values ​​between 0.36 and 0.81. The estimate using the Guldberg rule can deviate by up to 5000 K for metals. ${\displaystyle {\frac {T_{\mathrm {s} }}{T_{\mathrm {k} }}}}$

The Lydersen method tries to estimate the value of Θ for organic compounds more precisely on the basis of the chemical structure and thus achieves greater accuracy.

Typical conditions ${\displaystyle \mathrm {\frac {T_{S}}{T_{k}}} }$

	Normal boiling point	Critical temperature	relationship
mercury	629.88K	1750 K	0.36
tungsten	5828 K	13892 K	0.42
water	373 K	647 K	0.58
benzene	353 K	562 K	0.63
acetone	329 K	508 K	0.65
acetic acid	391 K	594 K	0.66
Ethanol	351 K	516 K	0.68
Nonane	424 K	595 K	0.71
helium	4.22 K	5.19K	0.81

literature

• CM Guldberg: About the laws of molecular volumes and boiling points . In: Z. Physics. Chem. , 5, 374, 1890.