Prologue:
Recently started with Chemical Kinetics at class. Came across a couple of points in Levine's Physical Chemistry (the book was recommended on Chem.SE; so I thought I'd give it a read :D) that I'm having serious issues wrapping my head around. This query is about the kinetics of equilibrium (and non-equilibrium) processes, and the fact that this has puzzled me for quite a while... I attribute to my (seriously questionable) understanding of equilibrium processes (courtesy: High-school education). It would be prudent to keep my shortcomings in Kinetics (newbie) and Equilibrium (possibly flawed understanding) in mind while addressing my query in your answer or the comments section. Thanks!
According to Physical Chemistry (Levine,I.N), Chapter 15, "Kinetics":
Processes in systems in equilibrium are reversible and are comparatively easy to treat. This chapter and the next deal with non-equilibrium processes, which are irreversible and hard to treat. The rate of a reversible process is infinitesimal. Irreversible processes occur at nonzero rates.
Which, if I understood correctly, can be paraphrased as:
Equilibrium processes are reversible and have infinitesimal (practically "non-existent") rates.
Non-equilibrium process are irreversible and have non-zero ("finite" or "significant"?) rates.
From my "understanding" of Equilibrium; chemical equilibrium is an example of dynamic equilibrium. When a chemical reaction, $$\ce{A + B -> C + D}$$
has proceeded to equilibrium. The "forward" rate of reaction (rate at which $C$ + $D$ is spit out) must equal the "backward" rate of reaction (rate at which $A$ + $B$ is spit out). There is no net formation of products/reactants, but both the forward and backward rates are positive and finite.
My question?
Why does Levine say that equilibrium processes have "infinitesimal" (almost non-existent) reaction rates? I thought the forward and backward reaction rates in a reaction at equilibrium are finite...