Fick's Law of Diffusion
by Greg Crowther
Fick says how quick
A molecule will diffuse.
Delta P times A times k
Over D is the law to use.
Fick says how quick
A molecule will diffuse.
Delta P times A times k
Over D is the law to use.
(Fick) Pressure difference,
(Fick) Surface area,
(Fick) And the constant k
Are multiplied together.
(Fick) They're divided by
(Fick) Diffusion barrier
(Fick) To determine the exact rate of diffusion.
A short song about the Fick equation as written in the form that governs the diffusion of gases. It was written for Biology 220 at the University of Washington. Ideally, "diffusion barrier" is pronounced so that it rhymes with "surface area." Also, the words "multiplied together" can be sung in harmony to reinforce the idea that factors are being multiplied.
When equations are expressed concisely, as in a jingle, the meaning of the abbreviations may be forgotten. “Fick’s Law of Diffusion” addresses this issue by presenting the abbreviations in the first half of the jingle, then spelling out the full terms (in the same order) in the second half. Thus, “delta P” corresponds to “pressure difference,” “A” corresponds to “surface area,” and “D” corresponds to “diffusion barrier.”
Questions: (1) Which term of the equation reflects a concentration gradient, which is necessary for diffusion? (2) What does the “constant” k depend on? Answers: (1) Pressure difference (delta P) refers to a difference in the partial pressures of a gas, and thus reflects a concentration gradient. (2) “Constant” k depends on the temperature, the size of the molecule that is diffusing, the specific medium through which it is diffusing (water? air?), etc.
• MP3 (demo)
• score (with melody playback)
• video
