# Le Chatelier's Principle Additional Practice

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## Objective

Students will be able to explain how a system in equilibrium shifts when a stress is applied by performing partner practice and a quiz.

#### Big Idea

Le Chatelier's Principle can be used to determine the direction in which an equilibrium system shifts when a stress is applied.

## Introduction

In this lesson students are practicing what they have learned about Le Chatelier's Principle to perform partner practice and a mini quiz.

• This lesson covers the Next Generation Science and Engineering Performance Expectation 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 learning about equilibrium and Le Chatelier's Principle.
• 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 of chemical equations to determine the effect of changes on equilibrium.
• 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 each pair of students needs either a whiteboard or a Le Chatelier's practice paper.

## Engage

10 minutes

I begin this lesson by reviewing the homework that students had two lessons previously (Equilibrium and Le Chatelier's Principle).

Normally homework is due the next day, but many students had problems with Le Chatelier's principle so I gave them an additional day to get the homework done.  What I did was give students a stamp if they had it done the day it was due but made it an extra credit stamp, and then gave students the extra day to get it done so students who had it done this second day also were able to earn a stamp for full credit.

Because a lot of students had a hard time with this homework I did not just put up the answer key, which I often do, but rather used a blank paper and went through each of the answers with students.  This movie shows how I did this with one of the problems.

Here is a copy of one student's completed homework.

This is a copy of the answer key.

## Elaborate

30 minutes

In this section of the lesson I have students do practice of Le Chatelier's Principle with a partner.  This activity is similar to when I use the strategy of Whiteboard Practice, but instead of whiteboards I have students use a prelabeled paper.

• I begin by instructing students to work with one partner (their elbow partner next to them or I help them move so that they are in pairs).
• I then pass out a paper to each pair.  This paper is made from this template.  The arrows on the template were not working well so I had to draw them in before I photocopies for students.  Also, I photocopy each side a different color and then pasted together so that students can fold the paper to either show that the reaction goes to the left or right and then whether the concentration increases or decreases.  This is a picture of what the arrows look like.
• I then introduce the activity to students.  This is a movie of me doing this in my classroom.
• I show students the PowerPoint where I ask them to analyze each system and then figure out which direction the equilibrium will shift or what will happen to the concentration of one of the reactants or products based on changes.
• When students have their answers they hold up their arrows and I give them a thumbs up or down for whether it is correct or not.
• For questions that are confusing for students I make sure to stop and go over why the correct answer is correct.   This movie shows how I do this in my classroom.

## Evaluate

5 minutes

As a way to conclude this lesson and to make sure that students are getting Le Chatelier's Principle I have them do a quick mini quiz.

The quiz consists of 3 questions, one in which the stress is a change in concentration, one for pressure, and one for temperature.

I collect the quiz and quickly grade using the Unit 9 quick quiz key.

For the most part students do well on the quiz.  The question that students struggled the most with was the pressure one.

Because so many students did poorly on the pressure question I made sure to review how to determine shifts when there are changes in pressure.  Also I made a point to make sure that there were multiple pressure questions on the Unit 9 Review.