Elephant toothpaste

Today's topic is the reaction typically known as elephant toothpaste.

It's a pretty simple reaction, the decomposition of hydrogen peroxide solution into water and oxygen gas.

H₂O_{2 (aq)} --> H₂O _(l) + O_{2 (g)}

This reaction happens all the time, most commonly in your home in that brown bottle of 3% hydrogen peroxide solution that somebody bought years ago and that goes 'pfsssst' whenever you open the cap.

The 'pfsssst' is the built-up oxygen gas.

In the demonstrations below (and after the jump with much bigger volumes), that reaction is catalyzed (sped up) by the addition of various things - typically sodium or potassium iodide but also yeast. And the oxygen gas is contained within soap bubbles.

Add that all together - maybe add in some food coloring - and you get a foamy mess.

...on Jimmy Kimmle's show...



...on The Big Bang Theory...



...a supposed world record volume...



...another supposed world record volume...



...another supposed world record volume...

A better description of entropy

I open my discussion of entropy in AP chemistry by saying that I'm going to offer an incorrect definition of entropy, that it's the same incorrect definition I was taught in high school and that my students will likely be told in college - as I was - that the high school definition isn't correct...that it's a drastic simplification.

I've said this for years, and I've had other people who study chemistry in college confirm that same story having happened to them, too.

I also will admit that I tried to read PF Atkins's The Second Law without much success.

So, let's try to be a little more precise and correct by watching Steve Mould's video up above - it's a video explaining how a Sterling engine works - and try to be better about what entropy really is.