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

Nicole Elhosni 2I
Posts: 62
Joined: Fri Sep 28, 2018 12:28 am

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

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?

Michael Torres 4I
Posts: 92
Joined: Thu May 10, 2018 3:00 am
Been upvoted: 1 time

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

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.

LilyL1C
Posts: 24
Joined: Fri Sep 28, 2018 12:20 am

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

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.