Rates of a Reaction and Factors that Affect a Reaction
Objective
Big Idea
Introduction
In this lesson students are introduced to the concept of reaction rates through watching a demonstration, asking questions, performing an exploration activity, and taking notes.
- This lesson covers the Next Generation Science and Engineering Performance Expectation 1-5: Apply scientific principles and evidence to provide an explanation about the effects of changing the temperature or concentration on the reacting particles on the rate at which a reaction occurs. It does so because students are learning about what happens in a chemical reaction and how factors affect the rate of chemical reactions.
- This lesson aligns with several of the Next Generation Science and Engineering Practices including:
- 1: Asking Question and Designing Solutions. It does so because students are coming up with their own questions based on the demonstration in the engage section.
- 2 Developing and Using Models. It does so because students are using papers to model what happens to reactants and products during a chemical reaction.
- 6: Constructing explanations: It does so because students are asked to answer the questions that they generated in the engage section using what they learned during the notes.
- This lesson aligns with several of the Next Generation Science and Engineering Crosscutting Concepts including:
- 1: Patterns. It does so because the pattern of reaction behavior can be studied and used to understand phenomenon.
For this lesson there are several resources needed:
- For the engage section teacher demonstration you need a container to put everything in, 3 100mL graduated cylinders, 1 25mL graduated cylinder, a scoop, 2 10mL graduated cylinders, 40mL of 3% hydrogen peroxide per class, 20mL of 30% hydrogen peroxide per class, 3 scoops of a detergent such as labtone per class, and 10mL of 2M sodium iodide per class.
- For the explore section each group of students needs 100 two-sided papers with Product on one side and Reactant on the other for the engage activity.
Engage
I engage students in the lesson by having them come up with questions regarding a phenomenon at the front of the classroom. I then have students come back to this phenomenon after taking notes to see if they can answer some of their questions. I like this activity because it is a fun demonstration that gets students interested in what we will be learning.
The demonstration that I do is based on Flinn Scientific's Sudsy Kinetics Lab Demo.
- I start by opening up the Unit9 lecture 1 PowerPoint and pass out to the unit9 intro demo paper students.
- I show students the first slide of the PowerPoint. And have them watch the demonstration. I tell them that as they are watching that they should record their observations in the first section of their intro paper.
- I then start by placing the hydrogen peroxide into the cylinders. 20mL of 3% into #1 and #2 and 20mL of 30% into #3.
- Then I place a scoop of Labtone detergent into all 3 (you could also use alconox or dawn).
- Finally I tell students to watch carefully and simultaneously place 5mL of 2M NaI into #2 and #3.
- Students watch as #3 foams up quickly and then #2 slowly foams up.
- I then tell students to come up with a list of at least 3 questions based on what they saw and to record on their papers.
- This is a video of me doing the demonstration.
- After students have recorded their questions I show them the 2nd slide of the PowerPoint which lists what was placed in the cylinders and then I have them come up with at least 2 more questions regarding the demonstration.
- After students have finished this I tell them to place their paper aside and that we will come back to it after our notes to see if we can answer some of their questions.
- Here are two examples of students work (Unit 9 intro student 1 and Unit 9 intro student 2). Notice how in example #1 the student draws what happens while in example #2 the students write it out. Also notice the difference in questions that they come up with where in example #1 the student has more detailed questions while in example #2 they are simpler.
Explore
For the next section of this lesson I have students begin to think about chemical reactions in terms of reactant concentration decreasing and product concentration increasing through performing and activity.
I got the idea for this activity from a workshop that I attended put on by Jodye Selco a professor at Cal Poly Pomona. This link has a website with more information about this activity.
- In my classroom I begin this activity by passing out a bag of 100 papers to each pair of two students. The set of papers has product written on one side and reactant on the other side. To make these papers I printed them in two different colors from the attached chem reaction visualization paper, glued them together and then cut them out. It would have been a lot easier to print on double sided paper, but I couldn't find any. After the fact one of my colleagues pointed out that I could shade one side darker and then print out on just white paper which is another great idea.
- I also pass out a copy of the chem reaction visualization paper to students.
- I then lead students in the activity.
- I tell them to take all of their papers and place on their tables with the reactant side facing up and to make sure that they have their calculators.
- I then show them how they will take a percentage of reactant and turn to product in each step. I also explain how they will then record how much reactant and product they have. This movie shows me doing this. This is a picture of students performing the activity.
- When students are done with the front side, they then flip their papers to the back and graph their data. This movie shows me explaining to student how to do this.
- When students are done graphing I have them summarize what they learned about the concentration of reactants and products in a chemical reaction which I show in this final video.
- This is a copy of the answer key and this is a copy of one student's work.
Explain
In this section of the lesson I introduce the concept of reactions, reactions rates, and factors that affect reactions to students. I do this by showing them a PowerPoint and students take notes on their notes graphic organizer.
- I begin by showing students slide 3 of the PowerPoint and have them review what they already know about chemical reactions. I give students several minutes to discuss with their groups and then go over the answers by calling on table groups. For the first question I get various responses including (reactants make products, bonds are broken, an irreversible change), for the second question most of them get that reactants make products (especially after having just done the intro activity), and for the final question I get varied responses. If students are stuck on the second question I tell them to think back to solutions and factors that affect a solute dissolving in a solvent.
- I then show students slide 4 and tell them that we will be learning about rates and factors that affect reaction rates.
- I explain to students about reactions and how you can graph them both in terms of concentration of reactants/products and energy of reactants/products. I go over how concentration changes on slides 5 and 6. I then go over how energy changes on slides 7 to 13. Along with talking about graphing I discuss collision theory, activated complexes, and exothermic/endothermic reactions.
- I then discuss factors that affect reaction rates on slides 14 -16. When I talk about catalysts I have students think back to biology and what they learned about enzymes.
- This is a copy of one student's filled in notes.
Elaborate
To finish the lesson I have students go back to their introduction paper and decide if they can answer any of the questions that they came up with.
I start by having students get out their unit9 intro demo student paper and show them the last slide of the PowerPoint.
I then have them go to #4 on their paper and have them try to come up with why there are differences in the three graduated cylinders. As students are answering the questions I walk around to make sure that they understand the question. For the most part students get that there is a difference in concentration between cylinders 2 and 3 so that is why 3 went faster.
I then show them #5 and have them think about what sodium iodide is. Most of them realize that it is a catalyst.
Finally for #6 I have them try to answer some of their questions. Most students are able to answer at least some of their questions.
Here are several examples of student work.
Unit 9 intro student 1, Unit 9 intro student 2, Unit 9 intro student 3
These examples are pretty characteristic of responses with students being able to understand the difference between the cylinders in terms of concentration and catalyst. Also, many students were able to answer some of their questions which was pretty neat!
