Gay Lussac and Combined Gas Laws

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Objective

Students will be able to describe the relationships between variables and solve problems using Gay Lussac's and The Combined Gas Laws as demonstrated through notes, making a foldable, and performing partner practice questions.

Big Idea

Gay Lussac's Law describes the relationship between temperature and pressure while The Combined Gas Law describes the relationship between temperature, pressure, and volume.

Introduction

In this lesson students continue their learning about gas laws through learning about Gay Lussac's Law and The Combined Gas Law.  Additionally they practice what they have already learned about Boyle's and Charles' Laws.

  • 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 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, T, & V) and solve problems using Gay Lussac's, Combined, 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 no additional resources needed.

Explain

30 minutes

To begin this lesson I jump right into teaching the two new equations for Gay Lussac's Law and The Combined Gas Law.  I present the notes on the PowerPoint while students fill in their answers on their graphic organizer.

  • I first teach students Gay Lussac's Law on slide 2.  While I go over this slide I have them predict what the graph will look like.  I encourage them to think about whether it will look like Charles' or Boyle's Law.  My goal is for them to see that because it also has a direct relationship that it will look like Charles' law and have a graph with a line that shows a direct relationship between pressure and temperature.
  • I then have students do the example on slide 3, making sure to remind them that temperature must be in Kelvin.  I review the answer on slides 4 through 5 making sure to reiterate the problem solving approach for isolating and then solving for the unknown variable.
  • Next I teach students the Combined Gas law on slide 6 and 7.  While I go over slide 7, I have students tell me the law that you get if you ignore one of the variables.  For example before I show 'ignore P and have Charles' Law' on the PowerPoint I ask students, "what gas law we have if we ignore P" and wait until they see that its Charles' Law before I show them the answer.
  • Students then have the opportunity to do the example question on slide 8.  When most students have tried the question I go over the answer using slides 9 and 10.
  • Here is an example of one student's filled in notes.

Elaborate Part I

20 minutes

After I have reviewed the Combined Gas Law and Gay Lussac's Law with students I have them make a foldable for the four gas laws (Boyle's, Charles', Gay Lussac's, and Combined).

  1. I first pass out students a pre-cut paper that has four flaps on the front. For for details on how I make these pre-cut papers and more information on foldables see my video and reflection on foldables in the introduction of my Matter lesson
  2. I then lead students to fill out the outside of their foldable by writing the four gas laws we learned, one on each flap.  I do this by showing them what I want them to do on the document camera at the front of the classroom.
  3. I then have students fill in information on the inside of each flap. I have them write down the equation, the variables, the constants, and a representative graph.
  4. Finally I have students flip to the back of their foldable and write down the likely units for each variable.  I added in this last part to the foldable because many of my students get confused as to which variable each unit belongs with.
  5. This is a picture of a completed Gas laws foldable.  Notice the outside, inside and back.

Elaborate Part II

40 minutes

After students have completed their foldable I give them time to practice using the equations by doing partner practice. 

  1. I begin by passing out the Partner Practice paper to students.
  2. I then give students time to make partners.  Here is a movie of my explaining Partner appointments to students.
  3. After I have give students about 5 minutes to find partners I then play matchmaker to ensure that all students have their partners.  I go through each appointment and have students raise their hands if they need a partner, I then match up the students with their hands raised.  If I have an odd-number class then I will have some students work as groups of 3.
  4. I then break students up and have them go to Partner #1 and Do question 2.  I do not necessarily go in the exact number of questions on the paper.  In this case I had students go back to number 1 if they had extra time so did not assign it with their partners.
  5. As students work on the questions I walk around to make sure that they are on task and working with their partners.  I also help out groups where both students are struggling.
  6. As soon as most students are done with the problem, I go over the answer on the document camera, have them thank their partners and then go to their next partner to do the next question.
  7. This is the answer key for the Partner Appointment paper.  Here are two examples (student 1 and student 2) of student work showing their partners and their strategies for completing the answers.

Evaluate

For the final part of the lesson I pass out student's Homework

  • I let them know that they are responsible for completing the homework on their own and that I will check it the next class.
  • At the next class I stamp the homework for completion and review using the answer key.
  • Here is one example of a student's completed homework.  Notice that this student did not isolate the variables first.  This is an issue I have with many of my students, especially the ones that are good in math.  As long as they get the correct answer I am okay with this; however, I tell them that as problems get more complicated that it ends up being easier to isolate the variable BEFORE plugging in the numbers.
  • The common mistakes on the homework include:
    • Not converting temperature to Kelvin
    • Forgetting to convert pressure in questions 2 and 4
    • Isolating the variables properly.