The Physical Basis of Biochemistry pp 445-454 | Cite as

# Flow in a Chemical Potential Field: Diffusion

Chapter

## Abstract

Transport is measured by
These named relations are:

*flux*, which is defined as the net movement of matter in unit time through a plane of unit area normal to the gradient of potential. In the case of*diffusion*, molecules of specific components will travel down their concentration gradient, ∂*c*/∂*x*, until the gradient is removed or neutralized. During*electrical conduction*, mass, as well as charge, is transported in an electric field ∂ψ/∂*x*. In aqueous solutions, the mass and charges are derived from either electrolyte ions or the autoproteolysis of water, which yields protons and hydroxyl groups. In*convection*, or fluid flow, molecules are moved by a streaming process caused by an external force ∂*P*/∂*x*, for example, pressure from a pump, as in the cardiovascular system or gravitational forces generated in a centrifuge.*Heat conduction*, caused by a difference in temperature ∂*T*/∂*x*, is also the result of a net flow, not of the total number of particles, which remains constant in the system, but of the particles with a higher kinetic energy. Each of these transport phenomena has a named relation of the form given earlier by:$$
{J_x} = - B\frac{{\partial A}}{{\partial x}} = - B{F_A}
$$

(27.1)

- 1.
for diffusion,

*Fick’s law*, and the constant is given as*D*, the*diffusion constant;* - 2.
for electrical conduction,

*Ohm’s law*with the constant κ, the*electrical conductivity;* - 3.
*for fluid movement, Poiseuille’s law*, and the constant,*C*, is a*hydraulic conductivity*related to the viscosity; - 4.
for heat flow,

*Fourier’s law*, and κ_{ τ }is the*thermal conductivity coefficient*.

## Keywords

Drag Force Intrinsic Viscosity Free Energy Change Thermal Conductivity Coefficient Chemical Potential Gradient
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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## Further Reading

- Bockris J. O’M., and Reddy A. K. N. (1970)
*Modern Electrochemistry*, vol. 1. Plenum, New York.Google Scholar

## Other Articles of Interest

- Einstein A. (1956)
*Investigations on the Theory of the Brownian Movement*. Dover Publications, New York.Google Scholar - Richards J. L. (1993) Viscosity and the shapes of macromolecules.
*J. Chem. Ed.*,**70**: 685–9.Google Scholar

## Copyright information

© Springer Science+Business Media New York 1998