+ Reaction Rates ! February 11 and 12, 2013 Boon Chemistry

+ Catalyst Review your grade report. List at least one strength and one thing you would like to improve. Did you do your homework during the Thermochemistry unit? How much time did you spend studying for the Thermochemistry exam? Did you use your green note sheet on the exam?  Objective I can define reaction rate and investigate factors that affect reaction rate.  Agenda  Catalyst  What is reaction rate?  Demo: Concentration  Investigation: Temperature  Practice: Reaction Rate

+ Shout Outs! (Period 5) The following students earned all 3’s and 4’s on the Temperature and Thermochemistry Exam: Alberto P., Brayllan R., Alejandro S. 11% proficient or advanced overall The following students scored a 3 or 4 on 3 of the four standards: Ruth B., Carol G., Daijah H., Jeremiah J., Brian M., Jonathan M., Alex P., Pablo R., Raven T., Xochi V. 48% of students showed at least 75% proficiency

+ Shout Outs! (Period 3) The following students earned all 3’s and 4’s on the Temperature and Thermochemistry Exam: Alejandra A., Irma C., Erik D., Douglas G., DeAndre G., Mario M., Emmanual P., Sandy P., Diana P., Billy V., Andres V. 39% proficient or advanced overall. The following students scored a 3 or 4 on 3 of the four standards: Rosie C., Gerardo G., Perla M., Chris O., Dalia R., Michael V. 60% of students showed at least 75% proficiency

+ Shout Outs! (Period 6) The following students earned all 3’s and 4’s on the Temperature and Thermochemistry Exam: Melissa A., Karim B., Monique F., Jose G., Jonathan L., Brian M., Kimberly R., Sereno R., Christine R., 32% proficient or advanced overall. The following students scored a 3 or 4 on 3 of the four standards: Kathy A., Daisy B., Kathy C., Kevin C., Clarissa C., Brenda C., Daniel G., Deya G., Sabrina M., Edward S., Alejandro V., Omar V. 75% of students showed at least 75% proficiency

+ Shout Outs! (Period 4) The following students earned all 3’s and 4’s on the Temperature and Thermochemistry Exam: Walter A., Leslie Al., Richard C., Maria C., Karla G., Kieman G., Michelle G., Patrick J., Abel M., Antonio O., Briceida P., Janet R. 41% proficient or advanced overall. The following students scored a 3 or 4 on 3 of the four standards: Ilsse A., Kevin A., Christina A., Lupe A., Jorge C., Vanessa C., Jessica G., Luis O., Cristina P., Abby R., Edgar S. 79% of students showed at least 75% proficiency

+ Shout Outs! (Period 2) The following students earned all 3’s and 4’s on the Temperature and Thermochemistry Exam: Jackie A., Susan C., Karen C., Saydy G., Zamir R. 21% proficient or advanced overall. The following students scored a 3 or 4 on 3 of the four standards: Edgardo A., Paola A., Tania C., Erick C., Melody C., Brandell C., Rumaldo G., Rudy M., Denise M., Christian R., Anthony S., Bernabe T., Ivan Z. 78% of students showed at least 75% proficiency

+ Start Up: Think Box (1) Give two examples of units that could be used to measure a car’s rate of motion. (2) What can you do to slow the rate at which milk spoils? You will have about 2 minutes to answer on your own. Then you will have about 1 minute to share.

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

+ What is reaction rate? A chemical reaction does not have one specific reaction rate. Rather, reaction rate is affected by many different conditions like concentration, temperature, surface area and pressure. Usually, the rate decreases gradually as the reaction continues. The rate is zero when the reaction is complete. Video: Reaction Rates vs. Dating 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?

+ Demonstration: Affect of Reactant Concentration on Reaction Rate The demonstration shows the relationship between reactant concentration and reaction rate. Summary of Procedure: (1) Two beakers contain aqueous KOH. Beaker 1 has a high concentration and Beaker 2 has a low concentration. (2) Add identical samples of aluminum to both beakers at the same time. (3) Observe the reaction.

+ Demonstration The Chemical Reaction: 2Al(s) + 2KOH(aq) ---> 2K[Al(OH) 4 ] + 3H 2 (g) (a) Label the reactants and products. (b) What reactant concentration will be varied? (c) What gas is produced? Hypothesis: How do you think the concentration of KOH will affect the reaction rate?

+ 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 KOH molecules there are dissolved in the water, the greater the chances that these molecules will collide with the aluminum foil. Conclusion: As reactant concentration increases, rate increases. As reactant concentration decreases, rate decreases.

+ Video: Affect of Surface Area on Reaction rate. The investigation shows the relationship between surface area and reaction rate. Conclusion: As surface are increases, rate increases. As surface area decreases, rate decreases.

+ Investigation: Affect of Temperature on Reaction Rate. The investigation shows the relationship between ___________ and ____________________.

+ 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.

+ Introduction to Chemiluminescence The chemical reaction: 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.

+ 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?

+ Explanation and Conclusion Explanation: As temperature increases, the proportion of molecules with enough energy to make a collision lead to a chemical reaction increases. The affect is not only about the increased number of collisions, but the increased energy of the collisions. Decreasing the temperature as the opposite effect. Conclusion: As temperature increases, rate increases. As temperature decreases, rate decreases_.

+ Using Balanced Chemical Equations to Express Reaction Rates. The reaction rate can be measured as the rate of appearance of a product or the rate of disappearance of a reactant. This means that there is more than one way to express the reaction rate of any chemical reaction. The rate expression must show the stoichiometric relationship between the reactants and products. So, the rate expression includes coefficients from the balanced chemical equation.

+ Example: The combustion of propane: C 3 H 8 + 5O 2  3CO 2 + 4H 2 O rate = - Δ [C 3 H 8 ] = - Δ [O 2 ] = Δ [CO 2 ] = Δ [H 2 O] Δ t 5 Δ t 3 Δ t 4 Δ t

+ Homework Read pp Pay particular attention to information about activation energy and catalysts. Problems pp. 595 #3, 4, 5, 9, 11, 14