Equilibrium Concentrations using I and K

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Equilibrium Concentrations using I and K

Postby JohnWalkiewicz2J » Sun Jan 12, 2020 7:02 pm

How do you go about solving for an equilibrium concentration for a product when only given the initial values of the reactants and the value of K?
Ex: Br2 + Cl2 = 2BrCl
Inital concentrations for reactants: 0.200 M
Kc = 7.20 @ 200 C

Niharika 1H
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Re: Equilibrium Concentrations using I and K

Postby Niharika 1H » Sun Jan 12, 2020 7:05 pm

You could solve for concentration of the product by using a RICE - Reactants, Initial, Change in Concentration, Equilibrium Concentration table, and leaving (x) as the concentration of the product. You would plug in the initial concentrations, and the equilibrium constant into the algebraic expression, found from Kc = [BrCl]^2/([Br]^2[Cl]^2).
Last edited by Niharika 1H on Sun Jan 12, 2020 7:17 pm, edited 2 times in total.

Kimberly Koo 2I
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Re: Equilibrium Concentrations using I and K

Postby Kimberly Koo 2I » Sun Jan 12, 2020 7:10 pm

To solve this, you use the ICEbox method. ICE stands for initial concentration, change in concentration, and equilibrium concentration. This method tries to create a quadratic equation where you can solve for the variable x. You would use the balanced chemical equation to represent the unknown change in concentration with the variable X. So in your example, the changes for each molecule would be (in order from left to right): -X, -X, and +2X. The equilibrium concentrations would be represented by the initial concentration +/- the change in concentration. So for the Br2 molecule, the equilibrium concentration would be 0.200-X. Then you plug each of your equilibrium concentrations in to the formula for K, set it equal to the given value of K, and algebraically manipulate K till you end up with a quadratic equation.

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Re: Equilibrium Concentrations using I and K

Postby Jielena_Bragasin2G » Sun Jan 12, 2020 7:14 pm

To solve this, you would create your chemical equilibrium expression with values that you can obtain from the equillibrium row of an equilibrium/I.C.E. table.
---In section 5I.3 in the book, they go into depth about equilibrium tables/I.C.E. tables; a summarized version is that in the initial row, you would place the initial molar concentrations of each reactant and product, the change row would contain the change in each molar concentration expressed in X, and the equilibrium row would contain the combination of the initial and change row---

You would then equal this expression to the K and solve.

You will eventually get a quadratic equation if you move the whole equation to one side, and you will solve this quadratic equation with the quadratic formula.The concentration cannot be negative or bigger than an initial condition. Plug in the fitting initial condition into the Xs in your equilibrium row to find the equilibrium concentrations.

I hope this helps !

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