Hess's law
Ley de Hess
- Date
- 1840 · confidence high
- Place
- Saint Petersburg, Russia
- Credited to
- Germain Henri Hess
- Field
- Matter & energy
What was discovered
Swiss-Russian chemist Germain Henri Hess published in Saint Petersburg, in 1840, the law of constant heat summation: the total heat released or absorbed in a chemical reaction is the same regardless of the steps or path followed, as long as the initial and final states are the same.
It is considered one of the earliest formulations of energy conservation applied to chemical reactions, before Joule and others formulated general thermodynamics.
What it led to
- the foundation of modern thermochemistry
- the basis for calculating reaction enthalpies via thermochemical cycles
- a direct forerunner of the first law of thermodynamics applied to chemistry