Maria Fokin Sep 22, 2014:

Dario, Secondo mio marito (un ricercatore pluriennale con dottorato di ricerca nel ambito di geochimica). Non c'è differenza "scientifica" neanche in Italiano. Ha detto che "all'equilibrio" è un po' più elegante e basta.
Secondo me, è meglio evitare fare affermazioni così categoriche. Buon lavoro.

Maria Fokin Sep 22, 2014:

The question is not whether "all'equilibrio" and "in equilibrio" is used different in Italian (of which I am not convinced), but rather whether the same difference apply in English.
The choice between the two prepositions comes down to 1) personal preference and 2) which sounds better in a given sentence.
The authors choice to use "at" means only that he likes it more. However, the fact that, despite this preference, he acknowledges the fact that the two prepositions mean the same thing, speaks volumes.
You sited Le Châtelier's Principle in your answer. Here is a discussion of this principle, in which the two prepositions are used interchangeably. If you do a search of scientific literature, you will find the same thing.

reaction in dynamic equilibrium
system in dynamic equilibrium
system is in equilibrium
reaction is at equilibrium
system at equilibrium
http://chemwiki.ucdavis.edu/Physical_Chemistry/Equilibria/Le...

dariomarti Sep 22, 2014:

The link you post here says "at (or in) equilibrium", admitting they're exchangable, at is out of parenthesis, in is inside. And the author uses in the entire document "at equilibrium". I suppose there is a meaning behind that, not only form...

Maria Fokin Sep 21, 2014:

When an equilibrium system has reached its point of balance, then we say that it has reached the “point of equilibrium” or that it is “at equilibrium” or “in equilibrium”.
http://noblereaction.org/gc/c35.pdf