Exploring Gas Laws: A deep Dive Into Gay-Lussac & the Combined Gas Laws

Exploring Gas Laws: A deep Dive Into Gay-Lussac & the Combined Gas Laws

Welcome back! This is part 2 of the Gas Laws mini-series where I'll highlight the framework and importance of Gay-Lussac’s Law and The Combined Gas Law and outline how you can take real-world examples of these concepts and explore them in your classroom!

If you missed it, go ahead and take a look at part 1 of the mini-series, Exploring Gas Laws: A Deep Dive into Boyle’s Law and Charles’s Law

I don't know about you, but for me, I think science classrooms should be the place where exploration and ideas lead learning, rather than using it to summarize what was presented. 

It’s tough as teachers when we have specific standards, concepts and testing dates to always prepare our students for. Sometimes we overlook the value in taking the extra time for more hands-on learning.

That’s exactly what you’ll find here! Understanding what each gas law states and how to demonstrate Gay-Lussac’s and The Combined Gas Laws to your students by infusing activities that are both engaging and applicable!

Recap of Previous Gas Laws

Last post we broke down and compared Boyle’s and Charles's Gas Laws using visuals and an organizer to review their concepts:

Here is a comparison chart that highlights the key aspects of Boyle’s Law & Charles’ Law:

Variables Involved

Mathematical Relationship

Constants & Conditions

Boyles’ Law

Volume (V)

Pressure (P)

P1xV1x = P2xV2

Temperature (T) is constant

Charles’ Law

Volume (V)

Temperature (T)

T1/V1 = T2/V2

Pressure (P) is constant

Part 2 of the mini-series will add in a third gas law, Gay-Lussac’s Law and lastly, tie in all three to discuss the Combined Gas Law.

Before we dive deep into them, I want to quickly define each and then we can explore the specifics and real-world concepts!

  • Gay-Lussc’s Gas Law: Demonstrates a relationship between pressure (P) & temperature (T) at constant volume.
  • Combined Gas law: Calculates the 3 variables pressure, temperature, and volume of a gas before and after a change is made OR uses the constant k to find one of the missing variables.

Gay-Lussac's Law: Pressure-Temperature Relationship

Gay-Lussac’s Law uses the formula (P1/T1 = P2/T2) and is similar to Charles’ Law in the sense that it shows a direct relationship. 

The greatest difference between the two is Charles’ Law explains the relationship between temperature and volume where Gay-Lussac’s Law explains the relationship between pressure and temperature.

Gay-Lussac’s Law Explained:

Simply put, as pressure increases, temperature must also increase in a container with a fixed volume. 

Now, the trick is how do we get our students to not just understand this concept, but to apply and identify this relationship in everyday life? Well…that’s where science demos come into play 🤓!

Real-life examples demonstrating Gay-Lussac's Law

♨️Pressure cooker: Using this kitchen appliance is a great start because this is something that students might have in their home and not even realize that because of Gay-Lussac’s law, they are able to have quick and delicious meals! Hence the name PRESSURE COOKER! 

🚗Car tires: If any students drive or have an interest in cars, then tapping into their hobby is an excellent way to connect science to real life. 

Changes in tire pressure and temperature is another demonstration of Gay-Lussac’s Law! Specifically if living in an area where there are distinct seasonal changes. Ideal PSI tends to fluctuate based on weather. During the winter months, PSI falls below normal and in summer months, tires overinflate due to higher temperatures. 

Classroom demonstration ideas

♨️Heating a sealed container: Consider bringing in a pressure cooker to  show a quick demonstration of what was shared as a real-life example. 

Another option is to demo an example of heating a sealed container while having students observe the pressure of the lid before and after.

🆒Cooling a sealed container: As a part 2 to heating a sealed container demonstration just mentioned, students can then observe the reverse: pressure decreasing as temperature decreases by observing the🕯️Tea Light Demo: When the candle goes out, the temp of the gas inside the container decreases which decreases the pressure and causes the water to be "sucked" into it.

A class favorite is detailed in the Exploring Gas Laws blog:

🥫The Crushing Can Demo: Heat water in a can to boiling, then turn it upside down into an ice bath. the rapid decrease in temperature will cause the can to crush itself due to the decrease in pressure.

NGSS Science and Engineering Practices (SEPs) and Crosscutting Concepts (CCCs)

⚙️SEPs & CCCs: Once you’ve presented a handful of demonstrations, try taking it a step further by having students explore these gas laws using the Animated Gas Lab from the Glenn Research Center at NASA

There are so many ways to incorporate this site into your lessons! 

  • Planning and carrying out investigations
  • Analyzing and interpreting data
  • Predicting changes in variables

Putting It All Together (The Combined Gas Law)

Last, but not least, we have the Combined Gas Law which essentially ties in Boyle’s, Charles’s and Gay-Lussac’s Law all in one!

The Combined Gas Law uses the formula P1V1/T1 = P2V2/T2 to demonstrate how each of the three gas laws all coincide into one comprehensive equation. 

Consider showing this diagram and asking students to brainstorm what they think the relationship between each of the variables is OR ask an observable question like:

🤔“How do hot air balloons work?” 

🤔“What do you think happens to a balloon when you let it go into the sky?”

Encourage students to use the diagram above as a model to help them explain their answer. The Combined Gas Law can be a bit tricky to grasp, so demonstrations and hands-on applications are a MUST for this one!

Don’t worry, keep reading to for the break down of a few of my favorite Combined Gas Law classroom demonstrations, simulators and worksheets! 

Connecting the Laws: Demonstration and Application

To help visualize the Combined Gas Law in action, you can build on those intro balloon questions by actually using balloons to observe what happens to the volume when varying temperature and/or pressure. 

Here’s what you’ll need for the Combined Gas Law Balloon 🎈demonstration:

1️⃣ Place an inflated balloon in the freezer well before the lesson

2️⃣ After discussing and ensuring students understand the Combined Gas Law concept, remove the balloon from the freezer for students to observe.

3️⃣ Remind students to take note of what happens when the temperature increases when at room temperature

4️⃣ Students will observe that the balloon gets larger as the gas inside the balloon starts to expand, showing the change in pressure.

Combined Gas Law Data collection and analysis:

If you’re looking for a Combined Gas Law worksheet  that allows students to practice:

  • Completing word problems in chemistry using the three variables, then this one-page review is the one you need!
  • Measure changes in pressure, volume and temperature
  • Applying the Combined Gas Law to calculate and predict gas behavior

…then this one-page review is exactly what you need! 

BONUS ⭐: This also comes with a detailed Answer Sheet!

Integrating the Combined Gas Law into Lessons

It’s important to remember that whether you teach Biology or Chemistry, gas laws can be integrated into either curriculum!

From part 1 of the Gas Laws mini-series and here with part 2, there are plenty of laid out demonstrations, engagement and review activities to fill a gas laws unit. 

When it comes to Biology, you might wonder if gas laws have a proper place and the answer is absolutely! 

Here are a few examples for how to apply gas laws into biology curriculum:

The key is making impactful connections! Biology is the perfect subject to apply gas laws that we can physiologically relate to:

  • Respiration and the human body 
  • Why do our ears pop in varying pressure changes
  • Scuba divers

If you’ve been part of the Keystone Science community long enough, then you know we can’t introduce a lesson without using phenomenon-based learning and NGSS aligned standards⤵️

Remember each of the Gay-Lussac and Combined gas laws demonstrations introduced earlier in this post? Well, those same demonstrations can essentially be used as an observable phenomenon.

A phenomenon is an observable event or concept that allows for students to use their observational skills to write what they saw, plausible explanations and any questions they might have about the phenomenon.

Here is a FREE Phenomenon handout complete with initial and extension questions, that can be used for any demo or introduction!

Integrating Demonstrations into Lessons

While our students might like the suspense of watching and waiting for the end result of a quick experiment or demonstration, there is so much more value than just their attention. 

By consistently using phenomena and hands-on demonstrations, it can make abstract concepts, like gas laws, more tangible and engaging for students.

I know it might feel like an additional step in your lesson planning, but I promise, once you have a set of introductory phenomena for each unit, then the hard part is done! 

All you need to do is create an outline of how the rest of the unit will play out. 

Speaking of outlines, I want to share with you my general outline of how I would go about creating a lesson on gas laws. 

Here is how I would tackle a Gay-Lussac’s Law & Combined Gas Law lesson plan:

➡️Introduction to gas laws AKA present a phenomenon 

➡️ Present a brief lecture to introduce gas laws concepts using the Gas Laws Unit Bundle  (which includes a PPT with guided notes!)

➡️Hands-on demonstrations of Gay-Lussac’s Law & Combined Gas law

➡️Data collection and analysis activities, an example would be the Mixed Gas Laws worksheet

➡️Group discussions and reflections on the observations and findings


Phew! We just tackled how to introduce Gay-Lussac’s and the Combined Gas law into a lesson and how to use classroom demonstrations to create more engagement and impactful connections. 

If you came here unsure of how to present these concepts, I hope now that you feel better prepared as far as structuring your lesson and knowing how to apply the Gas Laws Unit and activities! 

Even after teaching more than 10 years, I still find myself needing to revamp my curriculum and brainstorm with colleagues on how to help my students not just hear the lesson but really get it!

As long as the focus is kept on real-world examples, applications and engagement, then eventually comprehension will come. It might be at different points within a unit, but it will happen! 

If you are looking for fresh ideas and easy to use classroom strategies, then I know you will LOVE Keystone Science

To be the first to know when the next gas law mini-series post on Avogadro’s Law and the Ideal Gas Law is released and other tips, I would love for you to join the Keystone Science Community!

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