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### Calculating Equilibrium Concentrations when k < 10^-3

Posted: **Thu Jan 10, 2019 10:53 pm**

by **Nicole Elhosni 2I**

When we are using quadratics to find the equilibrium concentration, is it okay to assume that x in our ICE tables for the reactants is very small and thus the initial concentration - x = initial concentration? Or can we only assume this when it is a cubic function?

### Re: Calculating Equilibrium Concentrations when k < 10^-3

Posted: **Fri Jan 11, 2019 7:47 am**

by **Michael Torres 4I**

I believe you are free to make the approximation you mentioned both in quadratics and cubics. The source for my answer is question 5I.29. The equation would have ended up being a quadratic, but the solutions manual displayed usage of the aforementioned approximation.

### Re: Calculating Equilibrium Concentrations when k < 10^-3

Posted: **Fri Jan 11, 2019 8:14 pm**

by **LilyL1C**

I believe that as long as x is smaller than 10^-3, you can just use the initial concentration as the equilibrium concentration. And you can use it in both quadratics and cubics.