Space Shuttle Tile

Years ago, NASA gave away space shuttle tiles to educational institutions for demonstration purposes. One thing that amazed me when I first picked one up is how lightweight

it was - but I guess that makes sense if they needed to be launched into space. We still use them as props at outreach events.  I have included an optical micrograph of the glass fibers in the tile structure.  The black marks at the bottom of the picture are one millimeter apart.

Elastic Strip (Rubber Band or Balloon) Thermodynamics

Some elastic polymers heat up when they are stretched (and cool down again when they are allowed to relax back to their original position).  These temperature changes can be demonstrated by stretching thin polymer strips such as rubber bands, deflated balloons and even plastic grocery bags.  These temperature changes can be detected with thermometers that can monitor the temperature of surfaces or by placing the polymer strip against your upper lip - a temperature-sensitive body part.

The origin of this thermal behavior lies within the attractions between the chainlike molecules of the polymer.  In an unstretched polymer, the molecular chains are tangled like a plate of spaghetti.  In this tangled arrangement the molecules do have optimum contact (or optimum attraction) between the chains.  When the polymer is stretched, the molecular chains are pulled into alignment in the direction of stretching and have greater contact (and greater attraction) with each other.   When attractive forces are satisfied, energy is released.  In this case the energy is released in the form of heat.  When the polymer is released and the chains move back to their original position against their attractive forces, energy is consumed and the polymer cools down.

This polymer strip behavior can also be explained using more in-depth thermodynamic concepts such as enthalpy (H), temperature (T), entropy (S), and Gibbs free energy (G).  These concepts can be connected by the mathematical relationship that states that the change in Gibbs energy (G) for a process is equal to its change in enthalpy (H) minus the absolute temperature (T) multiplied by the change in entropy (S).  Stretching the strip is nonspontaneous, with a positive value of for its change in free energy, and its change in enthalpy must be negative, since the strip heats up and indicates an exothermic process.  Mathematically, its change in entropy must be negative.  This happens because as the strip is stretched and the molecular chains are pulled into alignment, the disorder within the plastic strip decreases.  Releasing the strip and allowing it to contract to its original shape is spontaneous with a negative change in free energy, and the change in enthalpy must be positive, since the strip cools down as it contracts.  Therefore the change in entropy must be positive.  This happens because as the strip relaxes and the molecular chains are moved out of alignment, the disorder within the elastic strip increases.

The pictures show a non-contact thermometer measuring the temperature of a relaxed and stretched deflated balloon.  Sorry about the rotated picture - there is a glitch in my software.

Ship Chemistry

I like big boats and I cannot lie...well, anyway, they are pretty neat.  Here is a picture of some decent-sized boats overwintering at Bay Ship in Sturgeon Bay, WI.  I recently read that these sorts of boats have lifespans of about 60 years, in contrast to saltwater boats that have a lifetime of about 20 years.  What a nice illustration of the corrosive effects of saltwater.  Another science-related concept is that of boat bouyancy and water temperature and salinity, as illustrated by Plimsoll lines.

Meteor Explosion

Thankfully, the meteor explosion over Russia this morning did not kill anybody, which makes it easier to talk about this likely once-in-a-lifetime event.  The data are still preliminary, but the meteor explosion, estimated to be maybe 500 kT, released enough energy to register as about a magnitude 2.7 earthquake on seismographs. The explosion registered on the USGS earthquake site (look for the cursor in the image).  Interestingly, today's likely stony meteor was estimated to be about 17 m in size, which is a little larger than some estimates for the size of the more dense iron meteor that made the Odessa impact crater (see the previous post). See also: http://www.space.com/19829-russian-fireball-meteor-blast-infographic.html and http://www.space.com/19838-russian-meteor-blast-bigger-size.html. Meanwhile, a larger asteroid passed quietly quite near the Earth today, as predicted.  Lots of potential teachable moments with all this data, at least for unit conversions.

Meteor Impact Demo Modifications

Years ago I learned a meteor impact demo from NASA.  In that demo, a layer of dark colored powder is placed over a layer of light colored powder.  A rock or marble "meteor" is dropped into the powder, which splashes the light colored powder up over the dark powder and makes ray patterns like meteor impacts on the moon (terrestrial impacts, like the one in Odessa, Texas, also show evidence of rock layers being bent up and over each other).  This is a fun demo to do, but with powdered layers it is hard to show the demo to a large audience, because you cannot easily tilt the layers to show the spectators without the layers collapsing.  I have been working on various approaches to solving this problem, and recently came up with using a dark cloth (rather than a dark powder layer) over a layer of light-colored flour.  The marble "meteor"cannot penetrate the cloth, so a hole must be made in the cloth.  To guide the marble to the fabric hole, it is dropped down a tube rather than simply through the air.  The tube (a plastic tube used to cover fluorescent light bulbs) can be held vertically or at an angle to show the effects of different impact angles. The flour splashed up from the hole fans out on the fabric.  The powder is held by the roughness of the fabric sufficiently well that the fabric can be carefully lifted up, but also loosely enough that the flour can be shaken out of the fabric to repeat the demonstration.  Thanks to my daughter Katie for helping with the demonstration.

A chemistry poem for Robert Burns Day

From the Journal of Chemical Education, 2007, vol. 84,  p.605.  More information about the poem is in the article itself.

This poem’s a tribute to Robert Burns

That praises Scottish chemists and their works in four turns.

I hope that you’ve all lowered the bar enough,

I’m a chem teacher, not a poet, but you might learn some stuff.

Joseph Black discovered carbon dioxide.

Without this gas our plants would have died.

Produced when carbon compounds burn,

Too much in the air is a global warming concern.

Black found latent heat would suffice

To explain boiling of water and melting of ice.

James Dewar developed his namesake flask

And for liquid gases it was up to the task.

It’s used today in your Thermos bottle…

…Your eyes are glazing over, so I won’t dawdle.

If I had to choose, if I had to guess,

I think Sir William Ramsay was among the best.

He had English colleagues, which isn’t so wrong.

We can be quite productive when we all get along.

Argon, neon, and others with like labels,

He added noble gases to our periodic tables.

Scottish pride likely hit new highs

When in 1904 he earned a Nobel Prize.

Finally there was Thomas Graham (not of cracker fame)

Who developed the law that now bears his name,

Which says that the rates of effusion of gases

Are inversely proportional to the square roots of their molar masses.

(We even cover this in our General Chemistry classes!)

We have students use this law in gas analysis,

But neglect to mention his gains with dialysis.

Over one million lives have been spared in this way.

His use of the word “colloid” remains to this day.

The word (meaning “glue-like”) can describe gel behavior

            Nanotechnology helps keep colloids in favor.

Four Scottish chemists whose fame involved gases.

Be thankful this poem is shorter than my classes!

Speaking of gases, if you think my air’s gone too far,

Note I wrote much of this in a car!

Ken Kolb's Birthday

Last night I attended an 85th birthday celebration for Ken Kolb, a professor at Bradley University.  He and his late wife, Doris, are big names in the area of chemistry education and both had a tremendous career at Bradley.  When I first interviewed for my job at Bradley, an associate where I was working at the University of Wisconsin-Madison said to me "You're going to the house of Kolb!"