What is the difference between Qsp and Ksp?

1 Answer
anor277
Feb 25, 2017

Well, K_"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, MX_n, certainly we can measure a constant for the equilibrium reaction for a given temperature:

MX_n(s) rightleftharpoonsM^(n+) + nX^-

And K_"sp"=[M^(n+)][X^-]^n

And likewise we so define Q=[M^(n+)][X^-]^n.

If Q=K_"sp", then equilibrium has been reached, and no MACROSCOPIC change will occur. If Q<K_"sp", then any precipitate will go up into solution. At Q>K_"sp", then precipitation will occur.

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