difusi

Difusi, also known as diffusion, is the net movement of particles from regions of higher concentration to regions of lower concentration, driven by random thermal motion. It occurs in gases, liquids, and solids and tends to equalize concentration over time. The process can be described quantitatively by Fick's laws. Fick's first law relates the diffusion flux to the concentration gradient: J = -D dC/dx, where J is the amount passing through a unit area per unit time, C is concentration, x is position, and D is the diffusion coefficient. Fick's second law, ∂C/∂t = D ∂^2C/∂x^2, describes how concentration changes with time in one dimension. D depends on temperature, the nature of the diffusing species, and the medium.

Difusi is often categorized as molecular diffusion, the spontaneous movement of molecules, and facilitated diffusion, which occurs across membranes via specific transport proteins without direct energy expenditure. Active transport, by contrast, uses energy to move substances against gradients.

Rate of diffusion is influenced by the concentration gradient magnitude, temperature, the diffusion distance, the area available for transfer, the size and mobility of diffusing molecules, and the viscosity of the medium.

Applications include gas exchange in respiration, spread of pollutants in air and water, and diffusion-driven processes in materials science and biology. Historically, diffusion concepts were formalized by Adolf Fick in the 19th century, forming a cornerstone of physical chemistry and transport phenomena.

See also: Brownian motion, diffusion coefficient, osmosis, dialysis.