Question

What does `K_(eq)` << 1 mean?

Answer 1

That the equilibrium favours the reactant side.

Explanation:

For the reaction,

`A+BrightleftharpoonsC+D`

There is a rate forward, `K_f[A][B]`, and a rate backward, `K_r[C][D]`

When `"rate forward"="rate backward"`, this is by definition the very condition of chemical equilibrium, which is characterized by an equilibrium constant, `K_"eq"`.

`K_"eq"=([C][D])/([A][B])` `=` `K_"f"/K_"r"`

And thus, when `K_"eq"` is small, it means that at equilibrium the reverse rate is much greater than the forward rate, and that the equilibrium favours the reactant side.