What is the Difference Between Mobility and Diffusion Coefficient?
🆚 Go to Comparative Table 🆚The key difference between mobility and diffusion coefficient lies in their definitions and the factors they depend on.
- Mobility is the ability of charged particles to move through a medium in response to an electric field. It is the ratio of the particle's terminal drift velocity to an applied force. Mobility can be separated into different types, such as electrical mobility for charged particles and hydrodynamic or thermal mobility for particles in fluid media.
- Diffusion Coefficient is a constant of proportionality between the molar flux (due to molecular motion) and the negative gradient of the concentration of the species or the applied force. The diffusion coefficient depends on factors such as the medium's viscosity and the size and shape of the particles.
The relationship between mobility and diffusion coefficient has been derived from the Langevin equation, which takes into account the random electric field caused by the motion of charged particles in a medium. According to the Einstein relation, the diffusion coefficient (D) is related to the electrical mobility (μ) and other factors such as the radius of the spherical particle and the dynamic viscosity.
In summary, mobility is the ability of charged particles to move through a medium due to an electric field, while the diffusion coefficient is a constant that relates the molar flux of a species to the applied force or concentration gradient. The two concepts are related through equations like the Langevin equation and the Einstein relation.
Comparative Table: Mobility vs Diffusion Coefficient
The key difference between mobility and diffusion coefficient is that mobility is the ability of charged particles to move through a medium as a response to an electric field, while the diffusion coefficient is a constant of proportionality between the molar flux (due to molecular diffusion) and the gradient of the concentration of the diffusing substance. Here is a table summarizing their differences:
| Property | Mobility | Diffusion Coefficient |
|---|---|---|
| Definition | Mobility is the ability of charged particles to move through a medium in response to an electric field. | The diffusion coefficient is a constant of proportionality between the molar flux (due to molecular diffusion) and the gradient of the concentration of the diffusing substance. |
| Unit of Measurement | Mobility is typically measured in cm²/V·s. | The diffusion coefficient is typically measured in m²/s. |
| Related Phenomena | Mobility is involved in processes like ion mobility spectrometry (in the gas phase) and electrophoresis (in the liquid state). | The diffusion coefficient is related to the process of diffusion, which is the movement of particles from a region of higher concentration to a region of lower concentration. |
In summary, mobility is the ability of charged particles to move through a medium in response to an electric field, while the diffusion coefficient is a constant that relates the molar flux of a diffusing substance to the gradient of its concentration.
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