Investigating Reaction Rates: Collisions and Energy

Time Required: 45 minutes Materials: Computer/tablet with internet access, Reaction Rates Simulation

Anchoring Phenomenon: Glow Sticks and Temperature

Have you ever noticed that a glow stick shines much brighter if you put it in hot water, but lasts much longer if you put it in the freezer? The light from a glow stick is the result of a chemical reaction. Why does the temperature of the environment affect how fast this chemical reaction happens?

1. Engage

Think about a crowded hallway between classes compared to an empty hallway after school. If you are walking down the hall, in which scenario are you more likely to bump into someone?

Chemical reactions happen when molecules bump into each other (collide). Today, you will investigate what factors increase the number of successful collisions, changing the rate of a chemical reaction.

2. Explore: Investigating Concentration

Open the Reaction Rates Simulation.

Set the Temperature to 300 K.
Set the Activation Energy to 50.
You will run three trials varying the starting concentrations of particles [A] and [B].
For each trial, click Start Experiment, wait for about 20 seconds, pause it, and record the average Rate (AB/s) from the data table. Make sure to click Reset and Clear Data between trials.

Data Table 1: Effect of Concentration

Trial	Initial [A]	Initial [B]
1	20	20
2	50	50
3	100	100

3. Explain: Concentration and Collisions

Analyze your data: As the concentration of particles [A] and [B] increased, what happened to the reaction rate?
Construct an Explanation: Using the idea of particles colliding, explain why changing the concentration had this effect. Use your data from Table 1 as evidence.

4. Explore: Investigating Temperature

Now investigate the effect of temperature.

Reset the simulation.
Set the Activation Energy to 50.
Set Initial [A] and Initial [B] both to 50.
Run three trials changing the Temperature. Record the average Rate (AB/s).

Data Table 2: Effect of Temperature

Trial	Temperature (K)	Average Rate (AB/s)
1	100
2	300
3	600

5. Elaborate and Evaluate: Putting it together

Analyze your data: As the temperature increased, what happened to the reaction rate?
Construct an Explanation: Temperature is a measure of average kinetic energy (how fast particles are moving). Using the idea of particle collisions, explain why increasing temperature changes the reaction rate. Use your data from Table 2 as evidence.
Application: Returning to the glow stick phenomenon, explain why a glow stick is brighter in hot water but lasts longer in cold water. Use the concepts of kinetic energy, collision frequency, and reaction rate in your answer.

Teacher Notes

NGSS Alignment

Performance Expectation: 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 Practice: Constructing Explanations and Designing Solutions
Disciplinary Core Idea: PS1.B: Chemical Reactions
Crosscutting Concept: Patterns

Evidence Statements Addressed:

Articulating the explanation of phenomena: Students construct an explanation that includes the idea that as kinetic energy increases and collisions increase, the reaction rate increases. (Addressed in Step 5.2 and 5.3 where students explain why temperature changes the rate).
Evidence: Students identify evidence from a table of data of a pattern that increases in concentration or temperature increase the reaction rate. (Addressed by having students generate Data Table 1 and Data Table 2, and referencing them in Steps 3.2 and 5.2).
Reasoning: Students use reasoning integrating evidence and scientific principles (molecules must collide to react, temperature means higher kinetic energy leading to more frequent collisions with enough energy to break bonds). (Addressed in Steps 3.2, 5.2, and 5.3 where students must connect collision frequency and energy to the observed rates).