Chemical Equilibrium and Le ChatelierŐs Principle Lab Report

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NAME

 

  1. Shifting Equilibria 1.  Explain why the equilibrium concentrations of the cobalt species appeared to change (or not) at each step.  Answer in terms of changes to the concentration of specific chemicals or changes in the value of K.

 

Step 3a

 

 

 

 

 

Step 3b

 

 

 

 

 

 

Step 3c

 

 

 

 

 

Step 3d

 

 

 

 

 

 

  1. Shifting Equilibria 2.  Explain why the equilibrium concentrations of the cobalt species appeared to change (or not) at each step.  Answer in terms of changes to the concentration of specific chemicals or changes in the value of K.

 

Step 4a

 

 

 

 

 

Step 4b

 

 

 

 

 

Step 4c

 

 

  1. Why do it?  Explain the purpose of the actions taken with beaker #3.  What did you learn from this set of experiments? (Hint: compare your results to those in Step 3.)

 

 

 

 

 

 

  1. Addition of Water.  Use examples from your data to describe how the addition of water to a solution affects the position of the equilibrium.  Explain why the addition of water changes the equilibrium position, even though [H2O] does not appear in the equilibrium constant expression.

 

 

  1.  Temperature Dependence of K.  Use your observations to explain why it is important to include the temperature when reporting the value of K.  Summarize the observations that you made as you changed the temperature of the cobalt solutions.

Write the chemical reaction for this equilibrium.

 

 

 

 

Does the value of K for this equilibrium increase or decrease as the temperature increases?

 

 

 

Does the value of ĆG◦ for the forward reaction as you have written it become more positive or more negative as the temperature increases?

 

 

 

  1. The Copper Complexes.  Write a chemical equation for the reaction taking place in each of steps 12, 13, and 14.  Identify the dominant copper species in the solution at the end of each step.

 

Step 12.  Adding ammonia

 

 

 

 

Step 13.  Adding HCl

 

 

 

 

Step 14.  Adding water

 

 

 

 

 

  1. Shifting Equilibria 3.  In step 15, what is the dominant copper species in solution at 0◦C and at 100◦C.  Write a chemical equation for the equilibrium between these two copper species.  Put the species found in the hot solution on the product side.  Suggest a brief explanation for why the dominant copper species in solution is different at high and at low temperature.  Consider what might be happening to the value of K.

 

Reaction

 

 

 

Dominant at 0◦C                                                  Dominant at 100◦C

 

Explanation:

 

 

 

 

 

 

 

 

 

  1. Concentration Effects.  What is the dominant copper species in solution after cooling in step 16?  If this is not the same as the dominant species found in this same solution at room temperature before you reduced the volume, give an explanation for the change.

 

Dominant copper species after step 16:

 

 

Explanation:

 

 

 

 

 

 

 

 

 

  1. Thermodynamics and Equilibrium

 

(i)              Write the chemical equation for the equilibrium investigated in Steps 7-9.  Put the halogenated metal complex on the product side.

 

 

 

 

 

 

For the equation as you wrote it, is the forward reaction endothermic or exothermic?  Explain your choice.

 

           

 

 

 

 

(ii)            Consider the equation you wrote in (i).  Does the forward reaction represent an increase or a decrease in the overall entropy of the system?  Is this a large or small change in entropy?

 

 

 

 

 

 

(iii)           Based on your answers to (i) and (ii), what would you expect the sign of ĆG?

 

 

 

 

(iv)           Based on your answers to (iii), would you expect the value of K to be greater or less than 1 at room temperature?

 

 

 

 

 

(v)             Explain how your experimental observations support or contradict your answer to (iv).