Molecular diffusion

Molecular diffusion is a fundamental process in physics and chemistry, describing the random motion of particles in a medium (such as a gas, liquid, or solid) due to their kinetic energy. This process results in the mixing of the particles, leading to a net transport of matter from regions of higher concentration to regions of lower concentration, a process known as diffusion.

Overview

Molecular diffusion is a result of the random thermal motion of particles, which was first postulated by Robert Brown in the 19th century. This motion results in a net flow of particles from regions of higher concentration to regions of lower concentration, until a state of equilibrium is reached.

The rate of diffusion is determined by several factors, including the size of the particles, the temperature of the medium, and the concentration gradient. The mathematical description of diffusion is given by Fick's laws of diffusion, which relate the diffusion flux to the concentration gradient.

Mechanism

The mechanism of molecular diffusion can be understood in terms of the kinetic theory of gases. According to this theory, particles are in constant random motion due to their thermal energy. This motion results in collisions between particles, which lead to a redistribution of their kinetic energy and a mixing of the particles.

In a system at equilibrium, there is no net flow of particles, as the random motion of the particles results in an equal number of particles moving in all directions. However, if there is a concentration gradient, there will be a net flow of particles from regions of higher concentration to regions of lower concentration.

Applications

Molecular diffusion has many applications in various fields, including physics, chemistry, biology, and engineering. For example, it is crucial in the transport of nutrients and waste products in biological systems, in the mixing of gases and liquids in chemical reactions, and in the spread of pollutants in the environment.

In chemical engineering, the principles of molecular diffusion are used to design and optimize processes such as distillation, absorption, and extraction. In medicine, understanding diffusion is important for drug delivery and the functioning of the human body at the cellular level.

See also

• Brownian motion
• Fick's laws of diffusion
• Mass transfer
• Osmosis

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  Molecular diffusion at micro and macro scales

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  Illustration of molecular diffusion

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  Self-diffusion process

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  Diffusion in a medium

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  Entropy and diffusion