DIFFUSION THROUGH A CELL MEMBRANE
For an active diffusion to occur, the temperature . Diffusion – Temperature Dependence (I) Plot of the logarithm of the diffusion coefficient vs. the reciprocal. Time and temperature dependence of impurity diffusion is measured in detail for several ZrTiCuNiBe (Cu,Ni)–Be phase diagram and differ only in their Be/Ti. The formula is: Below, thermal diffusivity of water at varying temperatures and 1 , 10 and bara (, and psia) are given in figures and tables. . Online calculator, figures and tables showing specific heat of liquid water at.
Sutherland has made a correction to Eq. Contemporary kinetic theory takes into account the intricate character of molecular interaction; molecules repel one another when they are close and attract one another at a distance.
For dilute gas mixtures, and assuming that the molecular collisions are only binary and elastic, that the motion of colliding molecules is in terms of classical mechanics, that quantum effects are absent, and, finally, intermolecular forces act only along the center line, the expression for the diffusion coefficient in a binary mixture is obtained by Bird, Hirshfelder and Curtiss. Wilke and Lee noted the coefficient 1. This accurate definition results in a better agreement between experimental and computed data.
A correlation formula obtained by Fuller, Schetter and Gittings by means of computer-aided correlation of experimental points, expressed as: Diffusion volumes of atoms and simple molecules In order to calculate the diffusion coefficient in multicomponent systems, Wilke used the Maxwell-Stefan equation to derive the expression where D'A is the diffusion coefficient of the component A in the mixture with B, C, As has been noted, diffusion in liquids encounters greater resistance and the diffusion coefficients for liquids lower than to times.
The constant b depends on the size of diffusing molecules: Introduction of the association parameter into the formula is brought about by the fact that associated molecules behave like large-size molecules and diffuse at a lower rate; the degree of association varying with mixture composition and with molecule types.
Therefore, Wilke and Chang presented the values for most widespread solvents: A semiempirical formula suggested by Scheibel, is worthy of attention. Reddy and Doraiswamy have suggested the equation where KRS varies depending on the ratio of molar volumes: All formulas suggested above for calculating the diffusion coefficient hold true for low-viscosity liquids. For a high-viscosity solvent, they are in great error and therefore inapplicable.
The temperature effect on the diffusion coefficient has been poorly studied so far.
The experimental data of Wilke and Chang give available evidence that the activation energy varies from The dependence of the diffusion coefficient on concentration of diffusing substance, strictly speaking, is a consequence of the fact that diffusion flow depends on the difference gradient of the thermodynamic potential of the system rather than concentration, i.
Passive diffusion of solute into a cell is linearly related to the concentration of solute outside the cell. Carrier proteins increase the rate of diffusion by allowing more solute to enter the cell.
Facilitated diffusion, however, approaches a maximum rate as the carrier proteins become saturated with solute. What is the slope of this line? What do increases or decreases in the slope mean biologically? Now assume the concentration gradient is a constant. Look at the equation for facilitated diffusion and find the horizontal asymptote. Try graphing this equation with different values for K.
- Mass diffusivity
- Thermal diffusivity
How does this change the concentration at which the carrier proteins are saturated? Scientific American Books, Inc. Sugar transport in the red blood cell: Structure-activity relationships in substrates and antagonists.