Summary

In this lesson students will participate in an inquiry-based lab approach to determine the activation energy of the chemiluminescent reaction in a lightstick. Students will use the Vernier LabQuest to collect data related to light and temperature for analysis using the Arrhenius equation.

Grade Level

High School

NGSS Alignment

This lesson plan will help prepare your students to meet the performance expectations in the following standards:

• HS-PS1-5: Apply scientific principles and evidence to provide an explanation about the effects of changing the temperature or concentration of the reacting particles on the rate at which a reaction occurs.
• Science and Engineering Practices:
  • Planning and Carrying Out Investigations
  • Analyzing and InterpretingData
  • Using Mathematical and Computational Thinking

AP Chemistry Curriculum Framework

This lab supports the following unit, topic and learning objective:

• Unit 5: Kinetics
  • Topic 5.6: Reaction Energy Profile
    • TRA-4.C: Represent the activation energy and overall energy change in an elementary reaction using a reaction energy profile.

Objectives

By the end of this lab, students should be able to

• Confidently use probe ware and a spreadsheet to collect and organize lab data.
• Indicate the effect that temperature has on the rate constant, k.
• Describe the relationships between activation energy, temperature and rate of reaction.

Chemistry Topics

This lab supports students’ understanding of

• Chemical Reactions
• Activation Energy
• Using linear relationships to determine experimental values
• Data Collection
• Data Analysis
• Light
• Electrons

Time

Teacher Preparation: 20 minutes (after materials are acquired)

Lesson: 2-3 hours (over two class periods)

Materials (per lab group)

• Cyalume SnapLight lightstick
• Cardboard box (8x8x8)
• Duct tape
• Modeling clay
• Hot plate
• LabQuest (which can measure two variables at the same time)
• Light intensity probe
• Temperature probe
• Thermometer(s)
• Assorted lab glassware
• Stoppers to fit lightstick
• Tools (scissors, X-ACTO knife)
• Chemwipes
• Computer for analysis

Safety

• Always wear safety goggles when handling chemicals in the lab.
• Students should wash their hands thoroughly before leaving the lab.
• When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals.
• Follow the teacher’s instructions for cleanup of materials and disposal of chemicals.

Teacher Notes

• This lab is appropriate for Honors, Pre AP, Chem II or AP Chemistry classes.
• This lab works well with 3 students per lab group, but can be done in pairs.

• Prelab assignment (15-20 minutes): This is assigned to be completed before coming to the lab for Day 1.
  • Read introductory page and prepare to discuss.
  • No other part of the lab packet is handed out at this time so that students do not get hints about how they will accomplish their task.
• Day 1 (~85 minute lab period): In the lab on Day 1, students gather in lab groups and discuss the information in the introductory page.The teacher should move around the classroom to help students if needed, but this is the initial inquiry event, and if at all possible students should make the discovery: Students must discover/recognize the “y = mx + b” components of the Arrhenius equation:

ln I = (-E_a/R) • 1/T + A

and that the Arrhenius equation can be used to find E_a by gathering data which will enable them to graph ln I on the “y” axis and 1/T (Kelvin) on the “x” axis. They must then see that they need to find the equation for the best fit straight line, and use the slope (-E_a/R) to calculate E_a. This is the part of the investigation in which students must apply their knowledge of algebra and the equation for a straight line to an equation describing a physical relationship.

• Students then make a general plan for their data-gathering procedure. The teacher checks the plan of each lab group, with questions which may lead to helpful refinements, but there is not a depth of detail at this point. The students then tape their boxes, using an unopened light stick to adjust their set-ups.
• Day 2 (~85 minute lab period): Prelab assignment on Experimental Design handout (written) to consider details of the procedure. (Completed before students come to the lab.) No other handouts are given at this time so that students will not be led into a particular procedure and can propose their own method of data-gathering.If the teacher wishes, the student background on chemiluminescence could be handed out as well.
• In the lab, the teacher should lead a class discussion based on the prelab assignment handout to promote thinking about details of data collection. Teacher input from literature and previous years can be given at this point.
• Reach consensus on some details. Depending on the amount of time available, students can try variations of the procedure as long as they have teacher approval. See “Additional helpful information”, below, for an example of a time-efficient, effective procedure. This should not be handed out to the students.
• Collect and process data. Students may change their plans, or details of their plans and set-ups as necessary. All other student handouts are given when data-gatheringis completed.
• Assign: reading of theory on chemiluminescence and lab report. A brief class discussion may be used to on a subsequent day to help students review reaction mechanisms and the movement of electrons in the production of light in the chemiluminescent reaction. The teacher may choose to add questions about this information to the lab report.
• It is not necessary that these lab days be consecutive days.
• Addition helpful information (regarding lab procedure:
  • This information was compiled from student suggestions and trial/error.
  • Be sure that box and clay are in place and you are ready to use the lightstick.
  • Snap stick, shake, and cut off top with Exacto knife. Wait 10 minutes before beginning data collection. While waiting, proceed with heating and LabQuest set-up.
  • Put temperature probe (or thermometer) into the lightstick and put the lightstick into a 400 mL beaker filled to the appropriate level with water.
  • Heat the water to no higher than 70 ^oC and lightstick to no higher than 65 ^oC. While heating, set up LabQuest for data collection. Note: when turning on the LabQuest, choose the option to calibrate the screen.
  • Place light intensity probe in Channel 1 and Temperature probe in Channel 2. Under Sensor Set-up, choose Light, 600 lux. Mode: Time Based. Collect data for 10 minutes every 10 seconds – 600 seconds and 60 data points.
  • When the temperature of the lightstick is 65 ^oC, quickly remove it from water bath, place the temperature probe in the lightstick if not already there, wipe the lightstick with Chemwipes, and anchor it in the box with clay. The lightstick should be right next to the light intensity probe.
  • Close box, exclude room light with duct tape, and collect data for Run 1. If time, reheat and collect data for Run 2.
  • Note: to collect data, check to be sure the settings are correct and then press the green arrow.
  • Save data onto LabQuest (File/Save)
  • Import to computer with Logger Pro or email as text file.
  • To email: Display data table on LabQuest, enable Wi-Fi, then (File/email/textfile). Change the subject appropriately.
  • Proceed with data analysis. (See student handout.)
  • This Lightstick may be disposed of in the trash basket.
• Expected Results:
  • The activation energy of the reaction in various Cyalume lightsticks was reported by Shakhishari as 56.4 kJ in a range of -5 to 50 ^oC. This value was obtained using a lightstick emerged in water baths of different temperatures and has been used as the accepted value for this lab report.
  • Bindel, using a computer interface and continuous collection of data while a heated lightstick cooled, found values between 49 and 66 kJ in a temperature range of about 25 – 55 ^oC.
  • The activation energy was found by Roser and McClusky to be 105 kJ, using data collected continuously with a CBL system.
  • According to Kuntzleman, et. al., “For safety reasons, substituted phenyl oxalate esters are used so as to prevent formation of phenol”.
• Reference information (for all student handouts)
  • Kuntzleman, T.S., Rohrer, K.; Schultz, E., J. Chem. Educ. 2012, 89, 910.
  • Shakhashiri, J. Z., Williams,L.G., Direen, G.E., and Francis, A., J. Chem. Educ. 1981, 58, 70-72.
  • Chemical Demonstrations: A Handbook for Teachers of Chemistry;
    Gilbert, G. L., Williams, L. G., Shakhashiri, B. Z., Dirreen, G. E. K. Juergens, F. H., Eds.; University of Wisconsin Press: Madison, WI, 1983; Vol. 1, pp 125−204.
  • Bindel T. H., J. Chem. Educ. 1996, 73, 356-358.
  • Roser, C. E.; McCluskey, C.L. J. Chem. Educ. 1999, 76, 1514-1515.
  • Salter, C.; Range, K.; Salter, G. J. Chem. Educ. 1999, 76, 84−85.
• Images (molecular structures used in this lesson can be found at the following:
  • 9,10-bis(phenylethynyl) anthracene: Chemspider
  • Chemiluminescence reaction mechanism: Gilbert, G. L.; Williams, L. G., Shakhashiri, B. Z.; Dirreen, G. E. K.; Juergens, F. H., Eds. Chemical Demonstrations: A Handbook for Teachers of Chemistry ; University of Wisconsin Press: Madison, WI, 1983; Vol. 1, pp 125−204.
• Additional background information of interest:
  • Compound Interest: The Chemistry of Glow Sticks
  • C&EN: What’s That Stuff? Light Sticks