Activation Energy (and exploding bags of Chlorine) - Periodic Table of Videos

The Professor discusses activation energy - and we flash some light onto bags of Chlorine and Hydrogen.
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[SWard-oeoj]

The shelves quietly burning in the background was a nice touch.

[BackYardScience]

Exploding bags of chlorine? Now you're talking my language!

[unmistified]

legend has it the prefessor has been sitting in the room for 24 weeks now

[protocol]

So, lotteries tend to be endothermic since the number of tickets you'd have to buy to ensure a win typically costs more than you'd win.

[ekscalybur]

Petition to get One Great VOOOSH! as an official measurement?

[jhonbus]

Exploding bags of chlorine made me say "Wow!", and then "Why's he doing it right over the fire exit!?"

[electronicsNmore]

Never knew liquid O2 was magnetic. You learn something new every day. :-)

[tenor]

Students who don't study, either have high activation energy levels or do not contain energy inside.

[cleanerben]

"and the answer is..."
The professor's hair emits a fire supression field?

[michaelmettie]

That guy is amazing at asking questions lol

[RC-]

2:03 I realize you have a lot of these cards, but this still seems cruel XD

[kdawg]

A hugely important example of a catalyzed reaction that has has huge activation energy but is also endothermic is the Haber-Bosch ammonia synthesis process. It's one of the most important discoveries in history, and has led to the 1-2 BILLION people (maybe more) being able to survive by making it possible to effectively pull nitrogen out of the air and put it back into the ground to be used as fertilizer.

3H2 + N2 = 2NH3 is an exothermic reaction, but it has such a high activation energy that it was basically impossible to keep it self-sustaining with heat alone. Haber discovered that an iron catalyst reduced the activation energy enough to allow the reaction to proceed at manageable conditions. Bosch is the one that scaled it up from bench scale experiments to industrial scale. This was over 100 years ago.

It's one heck of an extreme setup to make this happen. It's been a while since I built one of these, but if I remember correctly, temperatures in the reactor need to be anywhere from 900-1000F (482-538C) WITH the catalyst just to keep reaction going, because of the high activation energy. However, once you do get the reaction going, because it's exothermic, the heat released from the reaction sustains the reaction. Thus, you need some sort of independent source of heat (we used electric heaters) to initially kick off the reaction, but then you switch them offline when the reaction gets going and the system stabilizes.

It was an interesting engineering challenge, that's for sure. Even though the temps have to be that high, you want them to be as low as you can get, because the equilibrium ammonia yields are favored by lower temperatures because the reaction is exothermic. Because the number of product moles is half that of the reactant moles, higher pressures also favor greater yield. I think our reactor operated at 950F (510C) and around 2000 psi (138 bar), but probably 50% higher pressures would be preferable. There's are serious pressure vessel considerations when operating at considerations like that, though. The reactor has to be at least 9-Cr, 1-Mo steel to resist hydrogen embrittlement which increases with temperature. 304 or 316 stainless have better embrittlement resistance but have lower tensile strength, meaning a thicker vessel. And stainless may cost more depending on availability of materials. And then there's the fact that you have to cool the product stream down to about -20F (-29C) to liquefy and remove the ammonia before recycling the unreacted H2 and N2 back to the reactor and having to heat it back up to 950F. Lots of staged heat exchangers.

I basically designed and supervised the building of that entire system (it was a pilot plant but still fully functioning) myself...at the age of 27-28. That's not to flex on others; that's to say to my fellow engineers that you can do amazing things if you're willing to put in the effort to learn what's going on. Don't let anyone tell you that you that something's beyond your grasp. You'd be amazed how much you can learn if you just open a book and then keep asking yourself "And how does this work? And this. And this."

[IamRasheed]

The professor seems to be a catalyst for the chemistry outreach process.

[runcycleskixc]

5:42. How to bring a smile to Neil's face.

[bonzibuddy]

Neil is one of the most fascinating and mysterious figures of youtube and I wonder if he knows it

[dominicray]

1:54 Dinosaurs Attack card being burned, I'll take that as a Hi to the Tims! Why card #25 though? Feel like the classic #5 Homeroom Horror would be more fitting.

[SteveGuidi]

Burning a collectible "Dinosaurs Attack!" card @1:23 -- sacrilegious!

[alanna]

So happy to see Professor Poliakov! Hope to see him more !

[Feyangel]

I don't know why but the first 30s of the video had me slightly worried

[roberte]

"Why doesn't my hair start burning?" Professor, your hair is already on fire.