Boyle's and Charles' Laws

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Objective

Student will be able to explain the relationships between pressure/volume and temperature/volume and perform calculations using Boyle's and Charles' laws as demonstrated by activities, notes, and practice.

Big Idea

Boyle's Law describes the inverse relationship between pressure and volume while Charles' Law describes the direct relationship between temperature and volume.

Introduction

In this lesson students continue their learning about gas laws by learning Boyle's and Charles' laws.  I introduce these by first going over the relationship between the variables and then having students solve problems algebraically.

  • This lesson does not align with any specific NGSS Performance Expectation; however, it does align with the old California State Standards.  Additionally, I feel that understanding gas laws and the basics of earth's atmosphere are important for students to know and is a topic that is interesting and fun for students.
  • This lesson aligns with the Next Generation Science and Engineering Practice 2: Developing and Using Models.  It does so because students are challenged to come up with models of how gas particles relate to each other.
  • This lesson also aligns with the Next Generation Science and Engineering Practice 5: Using Mathematics and Computational Thinking. It does so because students are challenged to understand the mathematical relationship between variables (P &V, T&V) and solve problems using Charles' and Boyle's Laws.
  • This lesson aligns with the Next Generation Crosscutting Concept 3: Scale, Proportion, and Quantity.  It does so because students are challenged to think about gases, despite the fact that they cannot see them as well as understand how algebraic expressions can be used to understand the relationship between variables.

For this lesson there are several resources needed:

1. For the cartesian divers I use 2L soda bottles, plastic pipettes, and nuts.  You can also use ketchup packets for the divers.

2. For the Charles' law lab activity each group needs a 125mL Erlenmeyer flask, a 25mL graduated cylinder, a large balloon (12in), and a hot plate.

Engage

15 minutes

To engage students in the lesson I have them start to think about how pressure and volume are related by using Cartesian Divers. 

  • This movie explain how I make cartesian divers using a 2L soda bottle, water, a plastic pipette, and a metal nut.  It also explains how the Cartesian Divers work.
  • I begin by showing students the second slide of the PowerPoint and pass out the Cartesian Divers, at least one per table.  I make sure to tell students to not turn the bottles upside down (If they do the divers will be permanently sunk) and I have students begin to play with the divers.
  • I then tell them to try to answer the questions on their Unit 7 lecture 2 activities paper.
  • I give students about 5 minutes to play with the divers and try to answer the questions on their own.
  • I then stop the class and have groups share out their observations. 
  • In the end I lead students to the understanding that when pressure increases, the volume of air inside the diver goes down.  I explain that this is an inverse relationships and to keep the diver in mind when we are learning about Boyle's law today.
  • This is an example of one students work.  It is at the top of their activities paper.

Explain/Elaborate

60 minutes

This is the bulk of the lesson where I teach students about Boyle's and Charles' Laws.  I teach them through going through slides 3-19 of the PowerPoint and students fill in answer on their Unit 7 lecture 2 student notes graphic organizer.

I start with Boyle's Law:

  1. I begin with going over the relationship of Pressure and Volume for Boyle's Law on slides 3 and 4.
  2. I then show students the Microscopic Illustration of Boyle's Law movie so that they can visualize what happens with pressure and volume.
  3. I then show students slide 5 and 6 to go over Boyle's Law and how to calculate a missing pressure of volume algebraically.
  4. I lead students through example problems on slides 7-13 making sure to stress that they need to underline what they know, circle what they want, write the equation, isolate their variable and then solve for the unknown.  Here is a movie of me explaining this to my students while going over practice problem #2.

I then go into Charles' Law:

  1. I begin with going over the relationship between Temperature and Volume for Charles' Law on slide 14.
  2. I then show students the Microscopic Illustration of Charles Law movie so that they can better visualize the relationship between Temperature and Volume.
  3. I then show students slide 15 and go over how this is a direct relationship because the variables are on top of each other versus next to each other in Boyle's Law.  I also make sure to stress that temperature has to be in Kelvin because it is an absolute scale.
  4. We then do the practice questions on slides 16-19 of the PowerPoint.  I again make sure to stress to use problem solving techniques.  Also, many students need help with isolating variables in the denominator so I take time to review cross-multiplication with students.

This is an example of one student's filled in notes.

Extend

20 minutes

For this section of the lesson students have time to continue to think about Charles' Law by performing an experiment.  I introduce the experiment to students on the last slide of the PowerPoint .  The experiment is found on the second part of the Activities paper.

1. I first introduce the activity to students and review that because we are using glassware and hotplates that they must wear their safety goggles.

2. I then have students go up to their lab stations with their table groups.

3. At each station students have a 125 mL Erlenmeyer flask, a bottle of water, a balloon, and a hot plate.

4. As students are working I walk around to ensure that they are on task and answering the accompanying questions.

Here is an example of a student's answers to the activity.  Notice how this student is trying to also bring in the idea of pressure which makes this a little confusing.  I was aiming to have students just think about temperature and volume as in this second example.

Evaluate

10 minutes

For the last section of this lesson I have students begin their homework.

  • I do not expect students to have their homework complete by the end of the class, but I like to have them start in class in case there is any confusion.  I tell students to complete at home.
  • The next class period I stamp their homework for completion and review using the answer key
  • This is one example of a student's completed homework.
  • The biggest mistake that students make is forgetting to convert temperature to Kelvin with Charles' Law.  Additionally, there are some students who have a hard time with algebra, so they need additional support with how to isolate variables and plug in their answers.  I make note of this and continue to support them as we do more gas laws throughout the unit.