What is the formula for diffusion coefficient?


What is the formula for diffusion coefficient?

Diffusion coefficient is the proportionality factor D in Fick’s law (see Diffusion) by which the mass of a substance dM diffusing in time dt through the surface dF normal to the diffusion direction is proportional to the concentration gradient grad c of this substance: dM = −D grad c dF dt.

How do you find the diffusion coefficient of a gas?

The gas phase diffusion coefficient, DP, depends on the pressure of the bath gas (P, in the unit of Torr) and is related to the diffusivity (or pressure-independent diffusion coefficient), D (Torr cm2 s−1), by the following equation [16]: D=DP⋅P.

Why the diffusion coefficient equation is exponential?

Dependence on Other Properties That is, diffusion is faster in both hotter and more rarefied gases. Here, Ediff is an “activation energy of diffusion”; the exponential form of this relation means that diffusion coefficients in the solution phase can grow quickly with temperature.

What is the diffusion coefficient of NaCl?

For the NaCl solution having the concentration of 2M, the diffusion coefficient is approx. 2.2*10e-9 m^2/s.

What is diffusion coefficient in liquid?

The diffusion coefficient is a function of the fluid, size of the diffusing molecule (larger molecules diffuse more slowly), temperature, obstruction of diffusion by pore structure in sediments or other materials, and the rate of mixing of water.

Which statement is correct for Fick’s law?

According to Fick’s law of diffusion, “The molar flux due to diffusion is proportional to the concentration gradient”. The rate of change of concentration of the solution at a point in space is proportional to the second derivative of concentration with space.

What is the diffusion coefficient for sodium ion in water?

The diffusion coefficient of Na+ and Cl- ions in water, extracted from relevant data in Table 2, are found to be 1.33 x 10-5 cm2/s and 2.03 x 10-5 cm2/s respectively. These ionic diffusion coefficients do not take into consideration the effect of solvation of the water molecules on the ionic species.

What is Fick’s 1st law of diffusion?

Fick’s law states that the rate of diffusion of a substance across unit area (such as a surface or membrane) is proportional to the concentration gradient.