Reaction Rates !

1. Reaction Rates ! February 11 and 12, 2013 Boon Chemistry

2. Catalyst You will have about 2 minutes to answer on your own. Then you will have about 1 minute to share.

3. Objective • I can define reaction rate and investigate factors that affect reaction rate. • Agenda • Catalyst • Notes: Reaction Rate • Demonstrations & Mini-Lab: Factors affecting reaction rate • Practice: Reaction Rate Foldable

4. What is Reaction Rate? Rate = change over time • Reaction rate is the rate at which a chemical reaction takes place. • It is measured by the rate of production of productor disappearance of reactant.

5. What is reaction rate? • A chemical reaction does not have one specific reaction rate. Rather, reaction rateis affected by many different conditions like concentration, temperature, surface areaand pressure. • Usually, the rate decreasesgradually as the reaction continues. The rate is zerowhen the reaction is complete. Video: Reaction Rates vs. Dating -- http://www.youtube.com/watch?v=OttRV5ykP7A Discussion Question: What analogy does the video use to explain the factors that affect reaction rates? What factors affect reaction rates? Can you think of your own analogy?

6. Affect of Surface Area on Reaction rate. • The investigation shows the relationship between surface areaand reaction rate. • We have two beakers with 50 mL of vinegar. In beaker 1, we will put a whole antacid tablet. In beaker 2 we will put a ground up antacid tablet. • Hypothesis: How do you think the difference in surface area will affect reaction rate? • Record your observations in the space on your handout. • Conclusion:As surface are increases, rate increases. As surface area decreases, rate decreases.

7. Affect of Reactant Concentration on Reaction Rate • The demonstration shows the relationship between reactant concentrationand reaction rate. • The video shows the reaction of Hydrochloric acid and calcium carbonate (marble chips) • Each successive reaction uses a lower concentration of hydrochloric acid. • Record your observations in the space provided. • How does changing the concentration of reactants affect the rate of reaction?

8. Demonstration • The Chemical Reaction: • HCl + CaCO3 CO2 + H2O + CaCl2 • (a) Labelthereactantsandproducts. (b) Whatreactantconcentrationwillbevaried? (c) Whatgasisproduced?

9. Demonstration: Concentration and reaction rate • Explanation: In order for the reaction to take place, the reactant molecules need to come in contact with each other. The more HCl molecules there are dissolved in the water, the greater the chances that these molecules will collide with the marble chips. • Conclusion: As reactant concentration increases, rate increases. As reactant concentration decreases, rate decreases.

10. Investigation: Affect of Temperature on Reaction Rate. • The investigation shows the relationship between temperature and reaction rate.

11. Introduction to Chemiluminescence • In nature, an example of chemiluminescence would be the firefly, which very efficiently creates light through a chemical reaction. Through industrial chemistry we have also created a similar form of emission; however, it is still not as efficient as a firefly. The most common reaction used in novelty toys like glowsticks is that of Cyalume with hydrogen peroxide. Peroxides give off a lot of energy in chemical reactions, and therefore would be perfect for such a precise and efficient reaction.

12. Introduction to Chemiluminescence • The chemical reaction: • cyalume+ H2O2 + dye → trichlorophenol + 2CO2 + dye[♦]
 In the equation above the diamond [♦] represents the excited stage during which the chemicals give off light. In this investigation, we will study the affect of temperature on the rate of the chemiluminescence reaction.

13. Investigation • Summary of Procedure: (1) Submerge one light stick in a bath of cold water (about 10°C). (2) Submerge a second light stick in a bath of hot water (about 50°C). (3) Allow each light stick to reach the same temperature as its bath. (4) Remove the light sticks, and activate them. (5) In a dark corner of the room, observe and compare the light intensities of the two sticks. (6) Record your observations. • Hypothesis: How do you think the temperature of the glow stick will affect the reaction rate?

14. Explanation and Conclusion • Explanation: As temperatureincreases, theproportion of moleculeswithenoughenergytomake a collision lead to a chemicalreactionincreases. Theaffectisnotonlyabouttheincreasednumber of collisions, buttheincreasedenergy of thecollisions. Decreasingthetemperature as theoppositeeffect. • Conclusion: As temperature increases, rate increases. As temperature decreases, rate decreases_.

15. Reaction Rates Foldable • Fold and cut the foldable worksheet so that it has “doors.” • Use your notes to fill in as much information as you can in the foldable. • When you are done, go to edmodo.com and click on the brainrush game to check your understanding.

16. Reaction Rate Foldable • Fold the worksheet in half the long way so that it opens like a book. The question: “What is reaction rate and how is it measured?” should be at the top of the front cover. • Cut along the lines between the questions to make “doors” for your foldable. • Use your notes to fill in the blanks on the inside of the foldable. • When your foldable is complete, use it to practice the new vocabulary. • Additional practice: Read pp. 575-585 problems pp. 585 #1-13. • If you need help working on your phase change diagram project, you may work on that now. Please raise your hand if you have questions.

17. Homework • Read pp. 586-595. Pay particular attention to information about activation energy and catalysts. • Problems pp. 595 #3, 4, 5, 9, 11, 14 • Phase Change Diagram Project Due Wednesday March 12.