Diffusion, Atom or Molecule Random Movements
Diffusion is Random Movement of Molecules or Atoms, How It Happens
Oct 14, 2009
Diffusion is random. Diffusion is movement. A single dye drop, or a sugar cube, added to unstirred water or tea, or an alcohol and perfume mixture sprayed into the air, all share the same physical experience — they will diffuse. Diffusion may be overlooked or neglected, but it occurs everywhere and massively, and it is important. This scientific inquiry reviews diffusion.
Diffusion, Atom or Molecule Random Movements Defined
Diffusion is the random movement of molecules or atoms from one place to another. The examples below illustrate that diffusion is an event that can be studied and traced.
Dye drops, or sugar, in unstirred water, over a sufficient period of time, will diffuse completely throughout the water. Both the dye and sugar will become diluted (decrease in concentration, or amount per volume) as time progresses. As the dye diffuses, the intensity of the color decreases or fades. Given sufficient time and volume (space), the dye would diffuse so that no dye would be visible because of diffusion and the dilution.
Perfume in a small room will diffuse. Here, a gas – the vaporized perfume molecules – diffuses in a gas (air). When the perfume has diffused sufficiently its odor is no longer detectable. Many different gaseous molecules can be detected by a dog's olfactory sensory nerves at a sensitivity 1 to 10 million times greater than that of humans (hence the use of bloodhounds and other dogs to track for evidence, victims or criminal escapees). Canines and other animals are effective, living, gaseous diffusion detectors. Gaseous molecules in the environment alert animals to potential mates, predators and food.
Diffusion Movements, Properties and Characteristics
Diffusion has unique and special characteristics. Diffusion is:
- random — occurs with no predictable path, or direction.
- movement from high-density areas to low-density areas.
- a 3-D event with movements potentially occurring in any direction and any space — large or small.
- size dependent, small atoms and molecules diffuse faster than larger ones.
- temperature dependent — the higher the temperature, the greater the rate of diffusion.
- a universal event — occurs wherever molecules and atoms can move.
- a property of liquids, gasses or solids contained within other liquids or gasses.
- able to reach equilibrium and uniformity in small, confined spaces — diffusion still occurs, but the concentration essentially remains the same.
Diffusion is dependent upon the natural kinetic energy (heat) of gasses, liquids and solids.
Diffusion, Atom or Molecule Important Examples
Diffusion is so common and so unadorned that it is often overlooked. Nevertheless, diffusion is massive, and highly significant as exemplified below.
Oxygen and carbon dioxide diffuse in the lungs in opposite directions. Oxygen diffuses from the alveolar space (lung sacs) into lung tissue, and carbon dioxide diffuses from the lung tissue into the alveolar sacs.
Molecules of digested food in the small intestine diffuse across the intestinal membrane and into the surrounding tissues and blood vessels, then these food molecules are transported to all tissues of the body.
Toxins — introduced into animal tissues by a bite of an insect or snake for example, or digestive enzymes — released from insects biting and chewing on plants — clearly diffuse into the targeted animal or plant tissues.
Medicine (drugs) in pills also diffuse as do food molecules. The pill dissolves, releases the medicine and the drug diffuses across the intestinal membranes, and thence to tissues and blood vessels. Upon arrival at the delivery points, the medicine diffuses into other tissues of the body. Examples of important medicines include:
- pain relievers, such as aspirin, ibuprofin
- antibiotics (ampicillin, streptomycin, tetracycline)
- oral tolbutamide (Orinase)
- thyroid hormones (thyroxin)
- heart medicines (e.g., toprol, lisinopril)
and represent just a small fraction of a large list of medical compounds.
Diffusion, Summary Definition and Conclusions
Diffusion is random, molecular or atomic movement. It is more significant than most people know, or imagine.
Sources
Hill, J.W. and D.K. Kolb. 1995. Chemistry for Changing Times. Prentice-Hall Inc., Engelwood Cliffs, N.J.
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