Equilibrium and LeChatelier's Principle???? help

Question

1. Which describes a solution that contains a system at equilibrium? Explain your answer.

One in which the color of the solution is changing slowly, or one in which the color is not changing.

2. The following equilibrium is established when copper ions and bromide ions are placed in solution.

heat Cu(H2O)6 2 4 Br- 6 H2O CuBr4-2

The tube on the left contains only copper sulfate dissolved in solution. The tube on the right is the result of adding some potassium bromide solution. Given that the Cu(H2O)6 2 ion is blue and that the CuBr4-2 ion is green, answer the questions below.

a. What happened to the concentration of each of the ions when the KBr was added?

b. What would happen to the value of K?

c. Explain why the solution changed color.

d. Would the tube feel hot or cold when the KBr was added?

3. Consider the following equilibrium.

Mg(OH)2(s) Mg 2 2 OH-

The tube on the left contains Mg(OH)2(s) and water. A chemical has been added to cause the change shown in the tube on the right. Suggest a possibility for what chemical could have been added.

4. Methanol has the formula CH3OH and can be produced by the reaction of carbon monoxide with hydrogen gas.

CO 2 H2 CH3OH heat

In an attempt to maximize the yield of methanol (amount of methanol produced), a chemist would try to shift the equilibrium as far to the right as possible. Which of the following would accomplish this?

a. heating the mixture

b. adding an excess of carbon monoxide

c. removing the methanol as it is formed

d. adding a substance that reacts with carbon monoxide

Answer 1

1.  The solution where the color is changing slowly.  If the color is not changing, then the reaction has reached its end point.  The changing colors indicate that the reaction is shfiting forward and reverse.

2.  heat Cu(H2O)6 2 4 Br- <==> 6 H2O CuBr4-2

a.  The copper-water complex concentration decreases and he copper bromide ion concentration increases

b.  K does not change unless heat is changed

c.  The collor changed due to the reasons is 2a

d.  The temp would have initially decreased as reactants form products; however, at equilibrium the temp would have returned to its prior state

3.  Mg(OH)2(s) <==> Mg2+  +   2OH-

To forces the reaction to the right, you needed to remove some of the product ions.  Adding the cation from any transition metal salt would cause OH- to precip out of solution.

4.  CO +  2H2 <==> CH3OH heat

c.  If you remove a product, then the reaction shifts to create more product.