# When does chemical equilibrium result?

Aug 30, 2016

When the forward rate is equivalent to the reverse rate of reaction.

#### Explanation:

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

There is a rate forward, $=$ ${k}_{f} \left[A\right] \left[B\right]$,

And there is a reverse rate, $=$ ${k}_{r} \left[C\right] \left[D\right]$.

By definition, chemical equilibrium occurs when the forward rate is equivalent to the reverse rate:

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

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

The dimensionless constant, ${k}_{f} / {k}_{r}$, is also known as ${K}_{c}$, the thermodynamic equilibrium constant. This is usually a constant for given conditions.

Large values of ${K}_{c}$ clearly favour the product sides, whereas small values favour the reactant side. Much thermodynamic data have been recorded with respect to various chemical equilibria.