Vibration and Chemical Reaction

Name: Grant U.
Status: student
Grade: other
Location: Great Britain

Question: If you can shatter a glass by finding the right resonant 
frequency. At a molecular level can you shatter sugar to form a 
different set of molecules, like maybe ethanol and carbon dioxide?
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Glass will shatter because the resonant frequency is relatively low.  
To shatter it, you find the frequency that supplies a wavelength that is 
a exact fraction of the "bowl" of the glass (20 000 Hz, the highest 
frequency most people can hear, has a wavelength of about 1.5 cm in 
room temperature air).  The size of a molecule is, obviously, much 
smaller.  Sucrose, or table sugar, C12H22O11, on its longest length 
is about 2 micrometers across.  This corresponds to a frequency of 
150 000 000 Hz, so, at the minimum, that frequency would be required.  
To create a wave that was a fraction of that size, 300, 450 or 600 
million Hz would be required.  Since sound waves are generated by 
mechanical movement, and I do not know of any materials that could 
handle that kind of movement, it is not likely to happen in the near 
future. 

S. Crouch
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Hi Grant,

Great question - the short answer is that
although a number of talented physical chemists and
physicists have worked on this, success has
been very limited and there is currently
no way to routinely do what you suggest using a laser.
Basically it turns out to be very difficult to
control what happens to the energy when it flows from
a photon of light into a molecule.

If you use a search engine to look up "laser control of
chemical reactions" you will find, oh, a whole bunch of hits-
this is a current area of research in chemistry and
physics.

Best, 

Dr. Topper
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Glass, actually usually crystal, shatters because the impinging 
vibrations come into resonance with the macroscopic shape of the 
vessel. The vibrations set up standing waves that exceed the strength 
of the material. In the other cases you mention, for example a sugar 
cube, other processes occur. The classic example is to take a wintergreen -- 
flavored "Life Saver" and crack it with a sharp edge such as a knife or 
chisel. In a "dark-adapted" room you will see a "flash" when the candy 
ring shatters. I am not sure that the exact mechanism is well 
understood. In the case of a liquid, such as ethanol or water, if 
the intensity of a sound wave is sufficiently large, the rarefaction 
mode of the sound wave may exceed the vapor pressure of the liquid. 
When that happens a bubble rapidly expands and then collapses, producing 
an intense compression wave, called cavitation. This usually occurs at 
frequencies above the limit of the human ear, but not always. Because 
the collapse occurs so quickly, the local temperature can reach thousands 
of degrees, producing chemical reactions and the emission of 
electromagnetic radiation (light). So the three examples you address -- 
the goblet, the solid, and the fluid -- all produce chemical and/or 
physical changes, but by different mechanisms.

Vince Calder
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Grant,
 
The shattering of glass using a particular resonant frequency does 
not really brake molecular bonds. The glass shatters along the grain 
boundaries - where different individual (macro)crystals meet. In effect, 
you still have glass at the end of the process - albeit in small pieces. 
While it is possible to decompose molecules by supplying sufficient 
amounts of energy to break molecular bonds - the energy between 
carbon-carbon bonds are well known- the problem you will likely 
encounter is that it would be very difficult to tune the energy to 
just the frequency that would destroy only particular C-C or C-O bonds. 
Moreover, in the case of carbon dioxide, you would actually have to 
form C=O bonds. You are very likely going to get a mish-mash of 
different decomposition products. The other problem of supplying energy 
to break bonds is that even if you did form ethanol or carbon dioxide, 
you could also be supplying those products with the energy to break their 
bonds, so unless you deviced some way to extract the products out as soon 
as they were formed, you are likely to form a tarry mess of polymeric 
products, stable gases, and other organic compounds as formed products 
broke and reformed in myriad ways.
 
Greg (Roberto Gregorius)
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