How is the reaction rate related to equilibrium?

1 Answer
Dec 16, 2015

We need to distinguish between static and dynamic equilibrium.

The common equilibrium you see in chemistry is dynamic equilibrium:

The rate of the forward and reverse reactions are equal, thus resulting in no net change in the concentrations of products or reactants.

Example:

#"H"_2(g) + "I"_2(g) stackrel(k_1)(rightleftharpoons) 2"HI"(g)#
#color(white)(aaaaaaaaaaaa)^(k_(-1))#
where #k_(1) = k_(-1)#.

The less common "equilibrium" is static equilibrium:

A reaction has not occurred or has previously finished, yet no motion occurs at that time. The rate of a reaction in either direction at static equilibrium is #0#.

NOTE: this does NOT necessarily mean that the concentrations of products is equal to the concentrations of reactants.

Example:

#"C" ("graphite") -> "C" ("diamond") rightleftharpoons "C" ("diamond")#

Here, #["C" ("diamond")] > 0#, but #["C" ("graphite")] = 0#.