Explosively Fun Way to Learn About Gas Laws

I remember learning about the Gas Laws in high school. It was like a light went on. Gas Laws explain everything from how a perfume spreads around a room, to how a pressure cooker works.

We began our gas experiments for kids by simply turning on my Scentsy candle warmer. The kids and I sat at the table and chatted while the warmer heated up. 

"Did you know that tiny molecules of gas are all around us?" I asked Jay and Allie. "A molecule is like a teensy weensy puzzle piece floating around. They’re so small that we can’t see them. But we breathe them and we feel them on our skin. They can put themselves together like a puzzle to make lots of things: animals, oceans, people, trees. But in the air, they're really spread out."

Before long, we started to smell the candle wax from across the room. "Do you smell that?" I asked the kids. They nodded. "But how? The candle is way over there. Those tiny molecules of gas are floating across the room and reaching our noses."

The kids looked at me with wide eyes. This was mind-blowing. It's an example of Graham's Law, talking about how gas molecules diffuse based on their mass.

But our gas experiments for kids were just beginning. 

I took the kids outside. With us, we took a 2-liter bottle of diet soda, a roll of fruit Mentos, two index cards and some tape. I rolled up one of the index cards so it was just larger than the diameter of the Mentos roll, and taped it into a cylinder. Then we opened the 2-liter bottle and placed the other index card flat over the bottle mouth. Very carefully, I placed the rolled index card on top of the flat index card and stacked the Mentos inside it. Then I yanked the flat index card out and the Mentos went plunging into the soda.

EXPLOSION!

It was better than fireworks. Cheaper, and much safer.

"You see," I explained to the kids, "the soda has a whole bunch of little gas molecules hiding in the liquid. When we dropped the candy into the soda, the bubbles all wanted to find places to grab onto the candy. So they all came out of solution at once, pushing and shoving. Remember what it was like at the carnival when we were standing in line to get on the carousel and they finally opened the gates? Stampede. That’s just what the gas molecules were doing."

Congratulations! We've just demonstrated Henry's Law, which deals with the interaction between the partial pressure of a gas on top of a solution and the concentration of solute in the solution (in this case, dissolved gas). P = Kc. The Mentos create a nucleation site for gas molecules to come out of solution and form bubbles, which increases the pressure of the solution.

Someday, maybe in a high school or college chemistry class, our kids may perk up their ears and realize that they understand! All from a fun experiment they did as a kid.