1. Write the balanced equation. Use ONLY this equation to reference how the reactions below will shift. Consider whether there is an addition, a removal, or no effect to the reaction.
Co(H2O)6^2+ + 4Cl^- <--> CoCl4^2- + 6H2O
2. Write the equilibrium expression for the reaction. Be sure to consider how water is handled in the equilibrium expression. You may leave off the unit analysis in this case. By convention, no units are reported for K values.
K = [CoCl4^2-] / [Co(H2O)6^2+] [Cl^-]^4
3.Calculate the value of the equilibrium value (K) for the initial flask of CoCl2. (Show your work.)
How do I do this?
You didn't write all of the question. The reaction (only one was written) can't shift unless you do something to it. What did you add or remove?
BTW, you need to inform your prof that the sentence of "By convention, no units are reported for K values" is not necessary. The truth is that K HAS NO UNITS, by convention or otherwise. The numbers that go there are activities and activities have no units so K has no units. It is true that we usually use molarity to avoid calculating activities and since M has units that is often used as units for K but those are "pseudounits" (often called provisional units) since the numbers that should go there don't have units.
To calculate the value of the equilibrium constant (K), you need to know the concentrations of the reactants and products at equilibrium. Given that the initial flask contains CoCl2, you will need to determine the concentrations of each species in the equilibrium equation: Co(H2O)6^2+, Cl^-, CoCl4^2-, and H2O.
Here is the step-by-step calculation:
1. Let's assume the initial concentration of CoCl2 is 'x'.
2. Since Co(H2O)6^2+ and Cl^- have a stoichiometric ratio of 1:4, the concentration of Cl^- will be 4x.
3. According to the balanced equation, for every one Co(H2O)6^2+ molecule that reacts, one CoCl4^2- and six H2O molecules are formed. Therefore, the concentration of CoCl4^2- is equal to 'x' at equilibrium.
4. The concentration of water (H2O) does not appear in the equilibrium expression since it is a liquid and its concentration remains constant.
5. Now, substitute the concentrations into the equilibrium expression:
K = [CoCl4^2-] / [Co(H2O)6^2+][Cl^-]^4
= x / (x)(4x)^4
= x / 256x^5
6. Simplify the equation by canceling out the 'x' from the numerator and denominator:
K = 1 / 256x^4
Therefore, the equilibrium constant for the reaction with the given initial concentration of CoCl2 is 1 / 256x^4.