## ICE tables and the quadratic equation [ENDORSED]

romina_4C
Posts: 100
Joined: Thu Jul 11, 2019 12:17 am

### ICE tables and the quadratic equation

I remember in high school we learned that when doing ICE tables and having a the final concentration (in the ice table) being something like 3.00 - x, we would just approximate it to 3.00 or something like that. Is there any situation we would apply that approximation to in class or are we only using the quadratic equation to solve for x ?

Tanmay Singhal 1H
Posts: 143
Joined: Sat Jul 20, 2019 12:16 am

### Re: ICE tables and the quadratic equation

I believe you use the quadratic equation

PranaviKolla2B
Posts: 114
Joined: Fri Aug 30, 2019 12:17 am

### Re: ICE tables and the quadratic equation

How exactly do you use ICE tables?

Chem_Mod
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### Re: ICE tables and the quadratic equation  [ENDORSED]

romina_4C wrote:I remember in high school we learned that when doing ICE tables and having a the final concentration (in the ice table) being something like 3.00 - x, we would just approximate it to 3.00 or something like that. Is there any situation we would apply that approximation to in class or are we only using the quadratic equation to solve for x ?

You can make the "small x approximation" when your equilibrium constant is very small ie <10^-5. This is because the value of x will be very small compared to the other initial concentrations; we check this by using the 5% rule--the x value you obtain after solving must be less than 5% of the initial concentration. We mainly use this to simplify cubic equations into quadratic equations so we can use the quadratic formula to solve for x instead of trying to solve a cubic equation. You could use this equation with the quadratic equations as well, but keep in mind that this shortcut is not as accurate as using the quadratic formula.