For Chem 14B simplifying the cubic equation when K is small is part of the syllabus.

Solving cubic equations is not part of the syllabus. Therefore examples with large K and solving cubic equations will not occur in Chem 14B.

See my detailed Outlines.

Below is an example simplifying a cubic equation (which can be done whenever K < 10

^{-3}).

When K is smaller than 10

^{-3} then X is much smaller than the initial concentration, [I], and therefore: [I] - X is approximately equal to [I].

Note: X is not zero.

But X is much smaller than [I] and therefore the

difference is approximately the initial value.

For example, someone with $1 million gives $1,000 to someone with no money. The $1,000 is meaningful (not zero) to the person receiving it.

But initial - change is essentially the initial ($1 million - $1,000 is approximately $1 million).

In the above example the equilibrium constant is really small.