FLAMES AND EXPLOSIONS

Part 1

Student: "Are you going to talk about atoms and molecules?"

Presenter: "That's all we are going to talk about."

Content, Occasions, Location, Audiences, and Sponsors: Selections from Faraday Christmas Lectures by Henry A. Bent in Pittsburgh's Soldiers and Sailors Memorial Auditorium for Honor Students in Chemistry from Western Pennsylvania, Eastern Ohio, and Northern West Virginia, supported by the Society of Analytical Chemists of Pittsburgh, the Spectroscopy Society of Pittsburgh, and the Department of Chemistry, University of Pittsburgh.

Purpose. To spark interest in science in sparkable youths by safe execution of striking demonstration-experiments and their explanations in terms of kinetic-molecular theory.

Setting. A large stage beneath a high ceiling fronted by a colorful display of floating balloons, with half a dozen large rectangular tables supporting and surrounded by an array of demonstration equipment including: large tanks of gases (hydrogen, helium, oxygen, nitrogen, methane, and propane) chained to dollies, large fire extinguishers, fire blankets, explosion shields, protective metal shields for table tops, spare goggles, face masks, ear muffs, propane torches, bottle-rocket launching rods, cannons, large tall glass flasks, hot plates with magnetic stirrers, plastic buckets, a large Dewar of liquid nitrogen, a large chest of dry ice, a large fish bowl of rectangular cross section, a large bell jar, a Plexiglas-sided candle stair case, molecular models, posters, an overhead projector, bottles and cans of chemicals, &c. Also familiar things (used in unfamiliar ways), including: balloons, candles, tennis balls, pop bottles, kitchen pan, kitchen towel, air, and water. Briefly put, THE BIG THREE: Flammable Gases, Liquid Nitrogen, and Dry Ice and equipment to exhibit their behavior.

Hands-On/Eyes-On Anticipatory Events for an Arriving Audience: A Preview of Coming Attractions: Crushing by hand of liquid-nitrogen-cooled flowers; watching balloons containing or attached to flasks containing subliming dry ice expand (and burst); ignition of soap bubbles filled with hydrogen and hydrogen-oxygen mixtures; ignition of hand-held propane-filled soap bubbles; and a slide show of highlights of the life of Michael Faraday.

Dress Rehearsals. Attended by middle school students and their teachers and, one evening, the general public. The same demos work for all audiences. Chemistry is chemistry. Combustion of hydrogen is the same for middle schoolers as for senior scientists. One merely says different things about it, depending on the sophistication of an audience.

Presenters. Staff of a Department of Chemistry's Outreach Program. Usually included: the program's director, a post-doctoral fellow, a visiting professor, a high school teacher on sabbatical leave, several graduate and undergraduate students, and, to handle lights and recording equipment, several volunteers from SACP and SSP.

[Boxed statements] stand for posters or projected images, on a large screen.

Text statements in bold face are descriptions of demonstration-experiments.

Statements in small type are messages for the reader.

P1 Principal Presenter 1

P2 Principal Presenter 2

Host (Current chairman of the SACP/SSP Faraday Lecture Committee). Signals end of Anticipatory Events.. Tells youths standing in line (usually a long line) that ignitions of soap-bubbles filled with flammable gases will resume for interested individuals at the end of the main program. Thanks providers of equipment. Introduces PP1 and PP2, briefly!

P1 Welcome to Faraday Lecture 2000. It follows in the footsteps of Michael Faraday and his famous Christmas Lectures for Juvenile audiences at the Royal Institution about, in his words, The Chemical History of the Candle.

The star of our program is in this tank.

P1 places an arm around a tank of hydrogen.

We can learn a lot about it just by observing the character of its container. It has only curved surfaces, top and sides, and bottom, also, concave inward, so that the tank can be stood upright, if somewhat precariously, hence this chain.

P2 unchains the tank from its dolly and, with P1's help, exhibits its bottom.

P2 The tank is pretty heavy. One might guess that it has thick walls.

P1 Access to the tank's contents is by means of a valve, at its top, protected by this sturdy screw cap.

P1 unscrews the cap, revealing a valve, to which he attaches reducing valves, "to reduce the pressure in steps," and adds that -

Everything about the tank

curved surfaces
large mass
protected valve
dolly of moving it about
chain to its dolly

suggests the same thing.

P1The tank is designed to contain a gas at high pressure and, thus, many molecules. For, as you know, -

For ideal gases

PV = nRT
==>
n = P(V/RT).

Thus, for given V and T,
if P is large, then n,
population of molecules,
is large.

For gases, molecular population is proportional to pressure.

P1 So much we infer from the tank's shape and mass. As Yogi Berra has said, "You can observe a lot just by watching." The tank's gas is hydrogen.

P2 Evidently hydrogen molecules are not be very sticky toward each other.

P1 In fact, at any temperature merely 23 Celsius degrees, or more, above absolute zero hydrogen cannot be liquefied however high the pressure may be.

P2 The tank is chained to its dolly, as we noted, to lessen the chance that it might tip over.

P1 For, should that happen, the tank might snap off its valve if it struck something on the way down.

P2 Created would be a rocket.

P1 It's happened. One time a tank of hydrogen in a chemistry building fell over, snapped off its valve, took off down a long hall, and exited the building through a wall at the far end.

P2 Somewhat like this:

P2 inflates and releases a balloon.

P2 As air in the balloon exited one way, the balloon — by Newton's Law of Action and Reaction — moved in the opposite direction.

P1 It's an example of a general rule: Gases tend to expand from regions where their pressure is high (e.g., inside the balloon, somewhat) into regions where the gas pressure is lower (in an auditorium's space outside the balloon).

P2 Here's another example.

P2 inflates a balloon from the tank of hydrogen. Young children are fascinated by that event. They know that balloons don't self-inflate. Yet the person standing near it wasn't blowing into it.

P1 Hydrogen's principal physical property is that it has the lowest density of any known substance, suggested by the fact that a...