What does Kc have to be less than for you to estimate?

[Nathan Tran 4K]

What value does Kc have to be less than for you to estimate, meaning you can negate the -x term when employing ice method to solving for concentrations of products given initial reactant concentration? Is it less than 10^-3 or something else? Just making sure!

[Josephine Lu 4L]

if Kc<10^-3, then you can use the approximation and ignore x in the denominator

[Madeline Ho 1C]

You can also double check by calculating the percent ionization. If it's less than 5%, the approximation is valid.

[Arta Kasaeian 2C]

I would personally use the 5% rule (percent protonation should be less than this) to approximate.