# Reaction Rates and Equilibrium Computer and Graphing Practice

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## Objective

Student will be able to describe, model and diagram chemical reactions and explain what happens to systems in equilibrium when stressed as evidenced by computer and graphing activities.

#### Big Idea

In equilibrium systems, reactants and products have specific concentrations and energy. When equilibrium reactions are stressed the effects can be predicted using Le Chatelier's Principle.

## Introduction

In this lesson students have a chance to practice what they have learned about Le Chatelier's Principle, Collision Theory, and graphing of reactions through computer activities and graphing.

• This lesson covers several of the the Next Generation Science and Engineering Performance Expectations including
• 1-6: Refine the design of a chemical system by specifying a change in conditions that would produce increased amount of products at equilibrium.  It does so because students are reviewing how Le Chatelier's Principle works in a computer activity.
• 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 performing graphing and computer activities related to reaction rates.
• This lesson aligns with several of the Next Generation Science and Engineering Practices including:
• 2: Developing and Using Models.  It does so because students are using models through graphing and computer simulations to understand kinetics and equilibrium.
• 4: Analyzing and Interpreting Data: It does so because students are using data to perform graphs.
• 6: Constructing explanations: It does so because students are explaining the phenomenon that they see on their graphs and on the computer activites.
• This lesson aligns with several of the Next Generation Science and Engineering Crosscutting Concepts including:
•  4: Systems and System Models.  It does so because students are able to see how Le Chatelier's principle can be used as a model to see the effect on an equilibrium system.
• For this lesson there are not additional resources needed.

## Explain

5 minutes
• To begin the lesson I explain to students that they will be doing two different activities with a partner, each taking about 45 minutes.
• I have students choose one partner (unless there is not enough for only 2's and then I will have a group of 3) to work with.
• I then have students either start with the computer activities OR the graphing activities and then switch as they get done.
• This is a movie in which I explain to students how they will be doing the activities.  These activities are described further in the two subsequent sections.

## Elaborate Part I

45 minutes

For the first part of this lesson (or second, depending on which order the students do the activity) they are with a partner on the computers doing two different computer activities.

For the first activity they are reviewing Le Chatelier's Principle using a visual animation that both shows and explains what happens to systems when they are stressed.

• The paper for this activity is unit9 review computer lab.
• The website that students use is from the Essential Chemistry by Robert Wang.  When they go to the website they click on the Chapter 15 Le Chatelier's tab.
• This activity "talks" to students so it is helpful if they are able to listen to it with headphones on their own computers, but in my classroom with only 8 computers I have them sit close to the computer with just one partner and try to listen carefully.  If they have earbuds I let them share those as well which helps.  If students  have a hard time hearing the description of each I explain to them how they can replay what the person said by clicking back or refresh on the computer screen.

For the second activity students are working with a PhET simulation on visualizing molecular-level reactions.

• The paper for this activity is PhET reaction rates.
• I have students use the simulation that is already downloaded on my computers but is available on PhET's website
• The goal of this activity is just for students to really see how collisions have to happen with enough energy to surpass the activation energy inorder for reactions to occur.

This is a copy of an answer key for the computer activities and this is a copy of one student's work.

## Elaborate Part II

45 minutes

For the second part of this lesson (or first depending on the order which students are doing the activities) students are doing some graphing.

• They are graphing both concentration of reactants/products over time and energy of a reaction over time.
• I have them do both of these together because a lot of students get confused between graphs for energy and graphs for concentration.
• For the first graph, students are graphing energy vs. time for two different reactions on the unit9 Graphing energy versus time paper.  Most students do a fairly good job with this first graphing exercise as that it is a review of exothermic and endothermic reactions which they learned in unit 6 (energy).  The only common mistake is that students tend to be unsure of what it means to have a larger activation energy (that it takes more energy to get started) which is reflected in this student example.
• For the second graph, unit9 reaction rate practice, students graph concentration of reactants over time and reflect on reaction rates at the beginning versus the end of the reaction.  This is one student's work.  Overall, students have a much more difficult time with this as I talk about in the reflection below.
• Here is a copy of the answer keys for this work.