Question

How do you calculate the Keq of a reaction?

Answer 1

These are not `"calculated"`, but `"MEASURED"`.

Explanation:

For the reaction........

`A+BrightleftharpoonsC+D`

There is a `"rate forward"`, `k_f[A][B]`, where `k_f` is some constant....

And a `"rate backwards"`, `k_r[C][D]`, where `k_r` is some other constant....

Now, by definition, a condition of `"chemical equilibrium"` occurs not when chemical change ceases, but when there is equality of forward and reverse rates, and thus.........

`"rate backwards"`, `k_r[C][D]-="rate forwards"`, `k_f[A][B]`. And so we take the quotient......

`k_r/k_f=([C][D])/([A][B])`

We more commonly call the quotient `k_r/k_f`, `K_c`, the thermodynamic equilibrium constant.