So I have very short doubt that whether catalysts are considered when we say that an equilibrium is homogeneous or heterogenous, like in an aqueous equilibrium with only aqueous reactants and products a solid catalyst is added, by intuition and the definition given in some books (i.e for an equilibrium to be homogenous the reactant and products must all be in the same phase) this should be an homogeneous equilibrium but I haven't seen a precise answer to this question anywhere or a reason behind it.
1 Answer
$\begingroup$
$\endgroup$
5
The catalyst changes neither the equilibrium constant expression nor the magnitude of the constant. So if all species (reactant and products) are in the same phase, it is a homogenous equilibrium. Adding a catalyst in (or as) a different phase does not change that.
I don't have a specific reference for this, but catalysts change the kinetics rather than the thermodynamics of a reaction. Thus, adding a certain type of catalyst is not expected to change the description of the thermodynamics.
-
$\begingroup$ With the little chemical kinetics I knew I gave similar arguement as well, but on discussion with some other people they argued that catalysts may react with the reactants, so in some sense the equilibrium is no longer homogenous. Could you point out what's wrong with their arguement. $\endgroup$– bm27Commented Dec 28, 2023 at 17:51
-
$\begingroup$ The catalysis may be non-homogeneous, but the reaction is still homogenous, so its equilibrium is described like the non-catalyzed reaction. If you need a more specific answer, you should edit your question to make it more specific (which examples you are thinking of, which books you have consulted, etc). The catalyst always reacts with the reactants, so the reaction intermediates will be in a different phase, but the bulk of the reactants and products will not. $\endgroup$– Karsten ♦Commented Dec 28, 2023 at 18:03
-
$\begingroup$ I think I have understood what you said and don't need more specifics, but just one thing, why have we in the first place segregated homogenous and heterogenous equilibrium? This question has been lingering in my mind since this doubt arised. $\endgroup$– bm27Commented Dec 28, 2023 at 18:10
-
$\begingroup$ The concentration of pure liquids and solids don't change as the reaction goes on. Consequently, a heterogenous equilibrium might behave a bit differently than a homogeneous equilibrium. As you know, pure liquids and solids are treated differently in an equilibrium expression, which is related. $\endgroup$– Karsten ♦Commented Dec 28, 2023 at 20:03
-