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Diffusivity, mass diffusivity or diffusion coefficient is usually written as the proportionality constant between the molar flux due to molecular diffusion and the negative value of the gradient in the concentration of the species. More accurately, the diffusion coefficient times the local concentration is the proportionality constant between ...
J is the diffusion flux, of which the dimension is the amount of substance per unit area per unit time. J measures the amount of substance that will flow through a unit area during a unit time interval, D is the diffusion coefficient or diffusivity. Its dimension is area per unit time,
The self-diffusion coefficient of water has been experimentally determined with high accuracy and thus serves often as a reference value for measurements on other liquids. The self-diffusion coefficient of neat water is: 2.299·10 −9 m 2 ·s −1 at 25 °C and 1.261·10 −9 m 2 ·s −1 at 4 °C. [2]
The Warburg coefficient (or Warburg constant; denoted A W or σ) is the diffusion coefficient of ions in solution, associated to the Warburg element, Z W. The Warburg coefficient has units of Ω / seconds = Ω s − 1 / 2 {\displaystyle {\Omega }/{\sqrt {\text{seconds}}}={\Omega }s^{-1/2}}
The diffusion coefficient is the coefficient in the Fick's first law = /, where J is the diffusion flux (amount of substance) per unit area per unit time, n (for ideal mixtures) is the concentration, x is the position [length].
Diffusivity is a rate of diffusion, a measure of the rate at which particles or heat or fluids can spread. It is measured differently for different mediums. Diffusivity may refer to: Thermal diffusivity, diffusivity of heat; Diffusivity of mass: Mass diffusivity, molecular diffusivity (often called "diffusion coefficient")
The diffusion coefficient can be combined with the reaction equilibrium constant to get the final form of the equation, where is the permeability of the membrane. The relationship being P = K D {\displaystyle P=KD}
The Levich equation is written as: = where I L is the Levich current (A), n is the number of moles of electrons transferred in the half reaction (number), F is the Faraday constant (C/mol), A is the electrode area (cm 2), D is the diffusion coefficient (see Fick's law of diffusion) (cm 2 /s), ω is the angular rotation rate of the electrode (rad/s), ν is the kinematic viscosity (cm 2 /s), C ...