Le chatelier’s principle

4,030 views
3,803 views

Published on

0 Comments
1 Like
Statistics
Notes
  • Be the first to comment

No Downloads
Views
Total views
4,030
On SlideShare
0
From Embeds
0
Number of Embeds
0
Actions
Shares
0
Downloads
0
Comments
0
Likes
1
Embeds 0
No embeds

No notes for slide

Le chatelier’s principle

  1. 1. Equilibrium Reactions and LeChatelier’s Principle or “ I know what you did during recess”
  2. 2. Why? <ul><li>We have been using phenolphthalein indicator in our last two labs </li></ul><ul><li>How/why does phenolphthalein change from pink to clear and back? </li></ul><ul><li>To understand this concept we need to learn about a couple of things… </li></ul>
  3. 3. Equilibrium <ul><li>Equilibrium Reaction : the reactants form the products at the same rate the products form the reactants </li></ul><ul><li>Two most common occurrences: </li></ul><ul><ul><li>Gases in reactions </li></ul></ul><ul><ul><li>Chemicals that dissociate in water </li></ul></ul><ul><li>Designated with a double arrow </li></ul><ul><li>reactants products </li></ul>
  4. 4. Equilibrium is like a teeter-totter… <ul><li>Remember back to elementary school… </li></ul>Jason Claire
  5. 5. The Bully <ul><li>But what happens when the teeter-totter is out of balance? </li></ul>Claire Jason Sally Grrr!
  6. 6. Everybody’s Happy! <ul><li>How can all three kids play on the teeter-totter and be happy? </li></ul>Jason Claire Sally This is fun!!
  7. 7. LeChatelier’s Principle <ul><li>When a system at equilibrium is disturbed, the system will correct itself to restore equilibrium </li></ul>
  8. 8. Huh? <ul><li>An equilibrium reaction is just like our teeter-totter </li></ul><ul><li>When the kids were given a new set of conditions, they made it work </li></ul><ul><li>When a reaction is given a new set of conditions, it will make it work, too! </li></ul>
  9. 9. What do you mean? <ul><li>The teeter-totter was initially at equilibrium (Jason and Claire) </li></ul><ul><li>The equilibrium was disturbed (Sally) </li></ul><ul><li>The system fixed itself with a new equilibrium, even though it is different from the original equilibrium (all three) </li></ul>
  10. 10. What about the Lab? Test Tube #1 <ul><li>Fe +3 + SCN -  FeSCN +2 </li></ul>Test tube #1 was a pale orange color, which was representative of an equilibrium between both sides (clear) (red) Fe +3 Fe +3 FeSCN +2 FeSCN +2 SCN - SCN -
  11. 11. Test Tube #2: <ul><li>Fe +3 + SCN -  FeSCN +2 </li></ul>We added more Fe +3 ions to this tube, which causes the reaction to shift to the left Fe +3 Fe +3 Fe +3 Fe +3 FeSCN +2 FeSCN +2 SCN - SCN -
  12. 12. How did Tube #2 equalize? <ul><li>Fe +3 + SCN -  FeSCN +2 </li></ul>The shift to the left causes the reaction to produce more of the chemicals on the right, in this case, FeSCN +2 Therefore, we see the tube turn red! FeSCN +2 FeSCN +2 Fe +3 Fe +3 FeSCN +2 FeSCN +2
  13. 13. Test Tube #3: <ul><li>Fe +3 + SCN -  FeSCN +2 </li></ul>We added more SCN - ions to Test Tube #3, which causes the equilibrim to shift to the left side. SCN - SCN - SCN - SCN -
  14. 14. How did Tube #3 equalize? <ul><li>Fe +3 + SCN -  FeSCN +2 </li></ul>The shift to the left causes the reaction to produce more of the chemicals on the right, in this case, FeSCN +2 FeSCN +2 FeSCN +2 Therefore, we see the tube turn red!
  15. 15. What about Test Tube #4? <ul><li>Fe +3 + SCN -  FeSCN +2 </li></ul><ul><li>How did adding Cl - ions affect the equilibrium of the system? </li></ul>
  16. 16. Test Tube #4: <ul><li>Fe +3 + SCN -  FeSCN +2 </li></ul><ul><li>The addition of Cl - ions takes some of the Fe +3 ions out of the equilibrium system. </li></ul><ul><li>They are more attracted to the Fe +3 since is has a bigger charge than FeSCN +2 </li></ul>
  17. 17. How did Tube #4 equalize? <ul><li>Fe +3 + SCN -  FeSCN +2 </li></ul><ul><li>The removal of the Fe +3 ions causes some of the product (FeSCN +2 ) to break apart to replace them </li></ul><ul><li>This causes the SCN- ions to increase, causing an increase in the clear color </li></ul>
  18. 18. The rest of the lab… <ul><li>Answer the questions for Reactions 2 and 3 on your own </li></ul><ul><li>For Reaction #3 the abbreviation (ppt) represents the white cloudy substance in the test tubes </li></ul><ul><li>Have fun! </li></ul>

×