ICE box

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Valeria Viera 1B
Posts: 60
Joined: Fri Apr 06, 2018 11:05 am

ICE box

Postby Valeria Viera 1B » Sun Jan 20, 2019 6:19 pm

Can someone tell me when we would use the ice box, what are the steps to it and also
when is it better to assume x is a really small number instead of just using the quadratic formula? (Like 1.01-x becoming just 1.01 if we assume x is really tiny)

Nathaniel 2E
Posts: 27
Joined: Mon Jun 25, 2018 3:00 am

Re: ICE box

Postby Nathaniel 2E » Sun Jan 20, 2019 6:38 pm

We use ICE tables when we're calculating equilibrium concentrations for reactions and for reactions with weak acids or bases. Good rule of thumb is if you're given a K value or asked for a K value, you'll use an ICE table

General steps are to fill out your initial concentrations for all aqueous or gaseous parts of the reaction (usually a given number for reactants and 0 for products), display the change through adding x to the products and subtracting x from the reactants, multiplying x by the stoichiometric coefficients. Then, add/subtract change from the initials, and use these in an equilibrium coefficient expression to calculate what you are asked for.

We can assume x is negligibly small if our Ka value is less than 10^-3. This can be checked using the 5% rule at the end of your work, % protonation should be less than 5%. A good rule of thumb is that we won't be asked to solve complex cubic expression, so if leaving the x in would result in a complex expression like this, you have gone awry and need to simplify.

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