# What is "equal" in a chemical equilibrium?

Dec 8, 2016

The rate of the forward reaction as compared to the rate of the reverse reaction.

#### Explanation:

For the generalized equilibrium we have:

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

Now we have a rate forward,

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

The condition of chemical equilibrium is reached when,

$\text{rate forward "-=" rate backwards}$,

i.e. $\frac{\left[C\right] \left[D\right]}{\left[A\right] \left[B\right]} = {k}_{f} / {k}_{r} = {K}_{\text{eq}}$.

${K}_{\text{eq}}$ is the thermodynamic equilibrium constant, WHICH must be measured for a given reaction, and for a given temperature.