What is diffusion? (with photos)

The most common type of diffuser is an aroma lamp.

Broadly speaking, diffusion simply means the propagation of a substance or quality from an area of ​​relatively high concentration to an area of ​​lower concentration. The term is most commonly used to describe the process by which molecules of different types reach a uniform concentration after being initially distributed unevenly through their random motions. This is sometimes called molecular diffusion, and it plays a key role in many areas of physics, chemistry, and biology. It is closely related to the way cells absorb nutrients, so life could not exist without it. The term can also refer to the diffusion of heat or light, or, in the context of the social sciences, the diffusion of ideas or innovations through society.

Molecular Diffusion

Molecular diffusion plays a fundamental role in physics, chemistry and biology.

Molecules are in constant motion due to the presence of heat; even at extremely low temperatures, some thermal energy is present, giving the particles thermal motion. In solids, particles are held in a relatively rigid structure and cannot stray too far from their initial positions, but in liquids and gases, they are free to move in a less constrained manner. This motion is random, as the molecules are constantly bouncing off each other, so there is no general pattern. This random motion is what allows diffusion to take place. The rate at which the phenomenon occurs increases with temperature, as the speed at which the particles move increases.

If two different gases at the same temperature are brought into contact with each other, then, over time, the random motion of their molecules will cause them to mix until they are evenly distributed, without the influence of any external factors. A similar phenomenon can often be observed with two different liquids, but sometimes, due to chemical factors, the liquids do not mix. For example, adding vegetable oil to water will not result in diffusion. When a solid is dissolved in a liquid, its molecules diffuse throughout the liquid.

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In liquids that mix, diffusion can be observed if the liquids are of different colors. This phenomenon should not, however, be confused with convection or advection, which involves the movement of large volumes of fluid by currents that require a source of energy. Diffusion is a form of what scientists call passive transport, that is, movement that occurs without any additional energy required. In the oft-cited example of a drop of colored ink being added to a glass of water, much of the mixing that occurs is actually due to the currents created by the initial movement of the drop of ink under gravity. In experiments that eliminate this and similar effects, true diffusion can be observed; for example, colored water can be seen to diffuse through a gel, but this is a much slower process.

Importance for Life

Diffusion also plays a role in the processes involved in the life of a cell, particularly in the transport of nutrients, amino acids and other essential substances from one place to another. Osmosis, the process by which molecules are transported across the walls and membranes of individual plant and animal cells, is a form of diffusion. A cell wall is a selectively permeable membrane, or through which certain molecules can pass but others cannot. If, on one side of the membrane, there is a solution of high concentration, while on the other side there is the same solution at a lower concentration, the solvent will tend to move to the area of ​​​​higher concentration until the two solutions reach equilibrium. This can only occur if the molecules of the solute – the dissolved substance – are larger than those of the solvent. Smaller solvent molecules can pass through the membrane, while larger ones are too big for that and must remain on the other side.

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Other forms of diffusion

Diffusion can also mean the propagation of heat through a solid, although this is commonly referred to as conduction, and the propagation of light through a translucent substance – e.g. frosted glass in a lamp used to provide a “diffused” light that it is more pleasant to look at. Outside the context of physics, the term can be used to describe the dissemination of an innovative idea or technology through a population, through contact between people, compliance within a group, or the observation of benefits brought to others. people.

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