Guldberg's rule
The Guldberg rule states that the normal boiling point of a substance is around two thirds of the critical temperature :
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.
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
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.