bme314quiz3 - Diffusion is defined as the movement of...

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x C D J - = Diffusion is defined as the movement of solute molecules from a higher to a lower concentration gradient occurs by a “ random walk ” mechanism in which molecules are continually colliding with each other while moving “on average” towards a particular direction brownie in motion – “ random walk ” – random movement of a molecule by its energy state – molecules colliding with each other And gradually diffuse out as it goes on The diffusive flux Where dC/dx is the concentration gradient in the direction of solute movement And D is the constant of proportionality and is defined as the Diffusion constant or Diffusion coefficient Fick's First Law Fick's First Law is used in steady state  diffusion , when the  concentration within the diffusion volume does not change with respect to time (Jin=Jout). ∙  is the diffusion flux in dimensions of [( amount of  substance ) length-2 time-1], [mol m-2 s-1] ∙  is the diffusion coefficient or  diffusivity  in dimensions  of [length2 time-1], [m2 s-1] ∙   is the concentration in dimensions of [(amount of φ   substance) length-3], [mol m-3] ∙  is the position [length], [m] Movement of a solute in a random manner. Diffusive flux = mass per unit time Mathematically proportional to the concentration gradient Concentration gradient in the direction of the solute movement J is proportional to the concentration gradient, d = diffusion constant Diffusion constant depends on what the solute is, where it is (liquid, water, oil) A property of the solute, but depends on what the solute is Depends on temperature Diffusion prop. To energy you give it Provide heat energy, collides more, moves more
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z y x t C a y x J J z x J J z y J J z z z y y y x x x = + - - - - - - + + + ) ( ] [ ] [ ] [ ψ Negative sign in front? By convention, if movement is high to low, direction of solute movement, the concentration decreases You can find out what D is for a particular solvent, using this equation. You use microscopy techniques to follow its random movement over time. The root mean square displacement Square each, take the mean, and square root the answer If diffusion coeff. Is high -> diffuse much more distance If diffusion coeff. Is low diffuse much less Flux proportional to conc. Gradient What is missing from first law? What is not in the equation?
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This note was uploaded on 11/29/2010 for the course BME 314 taught by Professor Frey during the Fall '08 term at University of Texas.

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bme314quiz3 - Diffusion is defined as the movement of...

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