Stress (Le Chatelier's) Lab

Le Chatelier’s Principle (Equilibrium Stress)

Use the following link to for the experiments that follow: Link

Experiment 1: (use the link above)

Click on the cobalt system. You will be shown a chemical equilibrium reaction at the top of the page and a photograph of a purple solution surrounded by icons. Each icon is a adding or removing something from the equilibrium causing a stress to the equilibrium. A stress will shift equilibrium in the forward (making more products) or reverse (making more reactants) direction. DO NOT CLICK ON ANY OF THE ICONS YET! Answer the following questions first.

1. What color is the solution if reactants are present? What color is the solution if products are present?

2. Why is the solution purple at the beginning?

3. It this an endothermic or exothermic reaction? Explain.

4. Each of the icons around the test tube is a stress. List each of the stresses and identify if you thing the reaction will shift in the forward or reverse direction. It is ok if you get this wrong! You are predicting what you think.

Now you will click on each of the stresses. Clicking on each icon in turn will show a pair of photographs. The first one is a photograph of the solution as it was BEFORE the action indicated by the click, the second photograph is the change in solution as a RESULT of the action indicated by the click.

• • Copy the data table neatly into your lab book and complete the following in the chart:

    • In the top right hand side box, write the equilibrium (include the colors).

    • In the box next to the item you are adding, draw an arrow under the substance in the reaction that you are adding (Down if you are adding it / Up if you are removing it).

    • In the box next to the item you are adding, draw an arrow across the box showing if the reaction is moving in the forward or reverse direction based on the color it changes in the picture.

    • Compare to your guesses and see how you did! If you did poorly, hopefully as you complete each section you will improve your guesses.

Experiment 2: (use the link above)

Click on the chromate system. DO NOT CLICK ON ANY OF THE ICONS YET! Answer the following questions first.

1. What color is the solution if reactants are present? What color is the solution if products are present?

2. Why is the solution orange at the beginning?

3. Each of the icons around the test tube is a stress. List each of the stresses and identify if you thing the reaction will shift in the forward or reverse direction. It is ok if you get this wrong! You are predicting what you think.

Now you will click on each of the stresses and complete the chart the same way you did above.

Experiment 3: (use the link above)

Click on the nitrogen dioxide system. DO NOT CLICK ON ANY OF THE ICONS YET! Answer the following questions first.

1. What color is the solution if reactants are present? What color is the solution if products are present?

2. Why is the gas pale brown at the beginning?

3. It this an endothermic or exothermic reaction? Explain.

4. Each of the icons around the test tube is a stress. List each of the stresses and identify if you thing the reaction will shift in the forward or reverse direction. It is ok if you get this wrong! You are predicting what you think.

Now you will click on each of the stresses and complete the chart the same way you did above.

Experiment 4: (use the link above)

Click on the iron thiocyanate system. DO NOT CLICK ON ANY OF THE ICONS YET! Answer the following questions first.

1. What color is the solution if reactants are present? What color is the solution if products are present?

2. Why is the solution pale orange at the beginning?

3. It this an endothermic or exothermic reaction? Explain.

4. Each of the icons around the test tube is a stress. List each of the stresses and identify if you thing the reaction will shift in the forward or reverse direction. It is ok if you get this wrong! You are predicting what you think.

Now you will click on each of the stresses and complete the chart the same way you did above.