BR General Chemistry 3.28

[bonitanolita]

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How do we know when we can ignore the "shift term" in equilibrium calculations. For example when calculating the following problem, we can ignore the +2x term.

3.28 General Chemistry BR
CaCl2(s) --> Ca2+ (aq) + 2 Cl-
excess 0 .01
-x +x +2x
ignore x .01 + 2x

 

[Rabolisk]

If I understand you correctly, this is because 0.01 >> 2x (when x is determined). The starting excess concentration of chloride is so much greater than equilibrium concentration of calcium. Alternatively, the change in chloride concentration is so small compared to the starting concentration that you can ignore it.

 

[bonitanolita]

Thanks!