Question

What is the equilibrium constant formula?

Answer 1

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

Explanation:

And this describes the equilibrium reaction:

`A+BrightleftharpoonsC+D`

For the derivation, which depends on equality of `"the rate forwards"` with respect to the `"rates backwards"`, see this old answer. Note that `K_"eq"` must be measured, and it has been measured for a variety of reactions.