The redox equilibrium; weak and stong
A redox reaction often occurs in a reversible proces of the type: equilibrium (see module 08).
A reductor, after donating electrons, changes in a substance that, in its turn, can gain electrons again: an oxydator.
Ans, an oxidator in a redox reaction always becomes a reductor.
| couple 1: |
red 1 |
 |
ox 1 + electrons |
| couple 2: |
ox 2 + electrons |
|
red 2 |
| Total equation: |
red 1 + ox 2 |
|
ox 1 + red 2 |
Whoever studies (module 08) the equilibrium reactions, knows that an equilibrium very often has a 'one-side-position' (there are many more weaker substances), wether left or right.
Please know that there are in the same way weak oxidators and weak reductors.
The stronger an oxydator, the stronger the tendency of this oxydator to pick up electrons.
and of course:
The stronger a reductor, the stronger the tendency of this reductor to lose electrons.
In the tables you find the oxydators and reductor ordened in strenght.
The redox reaction occurs spontaneously if we join stronger substances that create weaker ones.
The opposite is possible, but only with help from outside (see further on).
So, being spontaneous or not depends directly on the strenght of the reactants.
In general we may say that a redox reaction is an equilibrium:
red1 + ox2 ox1 + red2
This equilibrium responds to the rules for chemical equilibria, for example that the stronger ones react in favor of the weaker ones.
In other words: if you join strong substances with enough energy, than the biggest part of those stronger substances will disappear (react) while the weaker substances appear in a spontaneous process.
Those weak products still maintain a weak tendency to react back in a revers reaction, but - weak as they are - they do not succeed very well.
You can also say: direct redox reactions occur if you join strong substances.
You can predict a redox reaction on ground of the position of the oxydator and reductor in the redox table.
General rule:
a redoxreaction occurs (spontaneously) if the oxidator has a higher position in table X than the reductor.
Behind this rule, something is hidden:
Of the oxidator is above the reductor, the products (in the next column of the table) are weaker ones.
And we know that they remain in an equilibrium.
If the reactants (red1 and ox2)are strong (stronger that the products ox1 and red2), a spontaneous redox reaction will occur, or: the equilibrium goes to the right, in favor of the products.
Of red1 and ox2 hardly remains a bit and often we do not even apply the double arrow symbol