# What is the difference between Qsp and Ksp?

Feb 25, 2017

Well, ${K}_{\text{sp}}$ is an actual equilibrium constant, that is experimentally measured..........

#### Explanation:

And $Q$, the so-called ion product, is a TRANSIENT, non-equilibrium value.

For a sparingly soluble salt, $M {X}_{n}$, certainly we can measure a constant for the equilibrium reaction for a given temperature:

$M {X}_{n} \left(s\right) r i g h t \le f t h a r p \infty n s {M}^{n +} + n {X}^{-}$

And ${K}_{\text{sp}} = \left[{M}^{n +}\right] {\left[{X}^{-}\right]}^{n}$

And likewise we so define $Q = \left[{M}^{n +}\right] {\left[{X}^{-}\right]}^{n}$.

If $Q = {K}_{\text{sp}}$, then equilibrium has been reached, and no MACROSCOPIC change will occur. If $Q < {K}_{\text{sp}}$, then any precipitate will go up into solution. At $Q > {K}_{\text{sp}}$, then precipitation will occur.