# When a reaction is at chemical equilibrium, what is true about the forward and reverse reactions?

Dec 10, 2016

The condition of equilibrium specifies equality between forward and reverse rates.

#### Explanation:

$A + B r i g h t \le f t h a r p \infty n s C + D$

There is a rate forward, ${k}_{f} \left[A\right] \left[B\right]$, and a rate backward, ${k}_{r} \left[C\right] \left[D\right]$.

At $\text{equilibrium}$ these rates are equal, i.e.

${k}_{f} \left[A\right] \left[B\right] = {k}_{r} \left[C\right] \left[D\right]$, on rearrangement,

${k}_{f} / {k}_{r} = \frac{\left[C\right] \left[D\right]}{\left[A\right] \left[B\right]}$

The quotient, ${k}_{f} / {k}_{r}$, is better know as ${K}_{\text{eq}}$, the equilibrium constant. It must be experimentally measured.