|Here is the data sheet for the experiment so far, with sample measurements taken but the calculation of the Equilibrium Constant (K) remaining to be done.|
| In order to calculate the equilibrium constant (K), you first need to calculate the equilibrium concentrations of your reactants from the product's equilibrium concentration and the initial concentrations of the reactants. Note that the initial concentrations of the reactants is 1/2 the value on the bottles since the total volume of the equilibrium mixture is twice as big as the 10.0 mL portions of the two reactant solutions that are mixed together.
We will use the fact that our reactants combine to form the product on a 1:1 molar ratio to calculate equilibrium concentration of the reactants. In other words, if x amount of product is formed, then x amount of reactant must be used up. The equilibrium concentration of our reactants must equal m-x for Fe3+ (where m is the initial concentration of Fe3+) and n-x for SCN- (where n is the initial concentration of SCN-).
For our values of the initial concentration of the reactants and equilibrium concentration of product, our equilibrium reactant concentrations are calculated as shown below.
[Fe3+] = 6.0 X 10-4 M - 34.4 X 10-5 M = 2.56 X 10-4 M
[SCN-] = 1.3 X 10-3 M - 34.4 X 10-5 M = 9.56 X 10-4 M
Now that the equilibrium concentrations of the products and reactants have been found, the equilibrium constant can be calculated as:
|Therefore the equilibrium constant for measurement #1 is 1.41 X 103 , (please notice that we did not do measurement #2, but you have to do a second measurement using the other SCN- #2 solution to complete the experiment).|