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7th grade ch. 2 sec. 3 controlling chemical reactions


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7th grade ch. 2 sec. 3 controlling chemical reactions

  1. 1. SEC. 3 CONTROLLING CHEMICAL REACTIONS Kitchen Chaos online activity
  2. 2. Every chemical reaction involves change of energy. <ul><ul><ul><li>exothermic reaction = releases energy in form of heat </li></ul></ul></ul><ul><ul><ul><li>endothermic reaction = absorbs energy </li></ul></ul></ul>
  3. 3. activation energy <ul><li>minimum amount of energy that has to be added to start a reaction </li></ul>
  4. 4. Factors that affect rate of chemical reactions concentration surface area temperature catalyst inhibitor
  5. 5. <ul><li>amount of material in a given volume of another material </li></ul>1. concentration =
  6. 6. 2. surface area
  7. 7. 3. temperature
  8. 9. <ul><li>4. catalysts = </li></ul><ul><li>lowers activation energy </li></ul><ul><ul><li>enzyme = biological catalyst </li></ul></ul>
  9. 10. Elephant's Toothpaste <ul><li>Materials </li></ul><ul><li>16 oz. empty plastic soda bottle (preferably with a narrow neck such as those made by Coca-Cola) </li></ul><ul><li>1/2 cup 20-volume hydrogen peroxide (20-volume is 6% solution, purchased from a beauty supply store) </li></ul><ul><li>Squirt of Dawn dish detergent </li></ul><ul><li>3-4 drops of food coloring </li></ul><ul><li>1 teaspoon yeast dissolved in ~2 tablespoons very warm water </li></ul><ul><li>Funnel </li></ul><ul><li>Foil cake pan with 2-inch sides </li></ul><ul><li>Lab goggles </li></ul><ul><li>Lab smock </li></ul><ul><li>1. At each student's place: cake pan, plastic bottle, Dawn in small cup, food coloring, funnel, goggles and smock, 1/2 cup peroxide, dissolved yeast mixture. 2. Stand up bottle in the center of the cake pan. Put funnel in opening. Add 3-4 drops of food coloring to the peroxide and pour the peroxide through the funnel into the bottle. Show a water molecule diagram and a peroxide molecule diagram, pointing to the extra oxygen that will be set free. 3. Add the Dawn detergent to the peroxide in the bottle. 4. Pour the yeast mixture into the bottle and quickly remove the funnel. 5. The students can touch the bottle to feel any changes that take place. Observations </li></ul><ul><li>The reaction creates foam that shoots up out of the bottle and pools in the pan. After a minute or so, it begins to come out in a moving stream that looks like toothpaste being squeezed our of a tube. The students can play with the foam as it is just soap and water with oxygen bubbles. The bottle will feel warm to the touch as this is an exothermic reaction. How does it work? </li></ul><ul><li>Talk about the addition of the yeast as a catalyst which makes the peroxide molecule release the oxygen atom faster. The teacher who submitted this experiment claims to have done this with hundreds of students from kindergarten through fifth grade and some adults who all loved the experiment. It is very easy and safe to do again at home using regular hydrogen peroxide from the drugstore. </li></ul>
  10. 11. CATALYSTS <ul><li>A catalyst is like adding a bit of magic to a reaction. </li></ul><ul><li>Reactions need a certain amount of energy to happen. </li></ul><ul><li>If they don't have it, oh well, the reaction probably can't happen. </li></ul><ul><li>A catalyst lowers the amount of energy needed so that a reaction can happen easier. </li></ul>
  11. 12. 5. inhibitor <ul><li>decreases rate of reaction </li></ul>
  12. 13. INHIBITORS <ul><li>Works exactly the opposite of catalysts. </li></ul><ul><li>Slow the rate of reaction. Sometimes they even stop the reaction completely. </li></ul><ul><li>You might be asking, &quot;Why would anyone need those?&quot; You could use an inhibitor to make the reaction slower and more controllable. </li></ul><ul><li>Without them, some reactions could keep going and going and going. If they did all of the molecules would be used up. That would be bad, especially in your body. </li></ul>
  13. 14. Did you catch all that?
  14. 15. inhibitor <ul><li>decreases rate of reaction </li></ul>
  15. 16. factors that affect rate of chemical reactions : <ul><li>Concentration </li></ul><ul><li>Surface area </li></ul><ul><li>Temperature </li></ul><ul><li>Catalysts (enzymes) </li></ul><ul><li>Inhibitors </li></ul>
  16. 17. <ul><li>catalysts = </li></ul><ul><li>lowers activation energy </li></ul>
  17. 18. <ul><ul><ul><li>endothermic reaction </li></ul></ul></ul><ul><ul><ul><li>type of reaction that absorbs energy </li></ul></ul></ul>
  18. 19. enzyme <ul><li>biological catalyst </li></ul>
  19. 20. <ul><li>exothermic reaction </li></ul><ul><li>type of reaction that releases energy in the form of heat </li></ul>
  20. 21. activation energy <ul><li>minimum amount of energy that has to be added to start a reaction </li></ul>
  21. 22. Exothermic reaction
  22. 23. Endothermic reaction
  23. 24. endothermic & exothermic reactions Observation magnesium sulfate (MgSO 4 ) & water calcium chloride (CaCl 2 ) & water Endothermic or Exothermic Prediction
  24. 25. Questions (write the questions) <ul><li>What is the temperature before and after each reaction? </li></ul><ul><li>Which reaction was endothermic? Why? </li></ul><ul><li>Which reaction was exothermic? Why? </li></ul><ul><li>Are the results of mixing the MgSO4 and the water a chemical change or a physical change? Explain. </li></ul>
  25. 26. 1. _____ Fe + _____ S  _____ FeS 2. _____ H 2 + _____ Cl 2  _____ HCl 3. _____ Mg + _____ O 2  _____ MgO 4. _____ O 2 + _____ H 2  _____ H 2 O 5. _____ HgO  _____ Hg + _____ O 2 Balance the following equations. Tell what kind of reaction it is (synthesis, decomposition, replacement)
  26. 27. Question: How does surface area affect the reaction speed of an object? <ul><li>Information: L x W X # of surfaces </li></ul><ul><li>Hypothesis: If the surface area increases, then the speed of the reaction will increase. </li></ul><ul><li>Variables: shape or size of tablet (independent) </li></ul><ul><li> size (type) of cup </li></ul><ul><li> amount of water </li></ul><ul><li> temp. of water </li></ul><ul><li> age of the tablet </li></ul><ul><li>& ingredients </li></ul><ul><li> </li></ul>Time Whole tablet Crushed tablet