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Encyclopedia > Diffusion
This article is about the physical mechanism of diffusion. For alternative meanings, see diffusion (disambiguation).
Schematic drawing of the effects of diffusion through a cell membrane.

Diffusion is the movement of particles of a substance from an area of high concentration to an area of low concentration, resulting in the uniform distribution of the substance. For example, diffusion of particles causes a net movement of particles from areas of higher concentration to areas of lower concentration until equilibrium is reached. This is simply the statistical outcome of random motion: diffusion is a spontaneous process (more familiarly known as a "passive" form of transport, rather than "active"). Diffusion can affect a variety of different quantities. Examples include diffusion of concentration, heat, or momentum. Diffusion increases entropy, decreasing Gibbs free energy, and therefore is thermodynamically favorable. Diffusion operates within the boundaries of the Second Law of Thermodynamics because it demonstrates nature's tendency to wind down, as evidenced by increasing entropy.[1] Image File history File links Broom_icon. ... Diffusion has several meanings: Diffusion is the spontaneous spreading of something such as particles, heat, or momentum. ... Image File history File links Simple_difussion_in_cell_membrane. ... Image File history File links Simple_difussion_in_cell_membrane. ... Look up cell membrane in Wiktionary, the free dictionary. ... A spontaneous process in chemical reaction terms is one which occurs with the system releasing free energy in some form (often, but not always, heat) and moving to a lower energy, hence more thermodynamically stable, state. ... Passive transport is a means of moving biochemicals, and other atomic or molecular substances, across membranes. ... Sodium-Potassium pump, an example of Primary active transport secondary active transport Active transport (sometimes called active uptake) is the mediated transport of biochemicals, and other atomic/molecular substances, across membranes. ... For a less technical and generally accessible introduction to the topic, see Introduction to entropy. ... In thermodynamics, the Gibbs free energy is a thermodynamic potential which measures the useful work obtainable from a closed thermodynamic system at a constant temperature and pressure. ... The second law of thermodynamics is an expression of the universal law of increasing entropy. ...


Diffusion can be described mathematically by the diffusion equation. This equation is derived from Fick's law, which states that the net movement of diffusing substance per unit area of section (the flux) is proportional to the concentration gradient (how steeply the concentration changes in space), and is toward lower concentration. (Thus if the concentration is uniform there will be no net motion.) The constant of proportionality is the diffusion coefficient, which depends on the diffusing species and the material through which diffusion occurs. Fick's law is an assumption that may not hold for a given diffusive system (e.g., the diffusion may depend on concentration in addition to concentration gradient), in which case the motion would not be described by the normal (simple, Fickian) diffusion equation. An analogous statement of Fick's law, for heat instead of concentration, is Fourier's law. The heat equation or diffusion equation is an important partial differential equation which describes the variation of temperature in a given region over time. ... Ficks laws of diffusion describe diffusion. ... flux in science and mathematics. ... Heat flow along perfectly insulated wire Heat conduction is the transmission of heat across matter. ...


Diffusion can also be described using discrete quantities (the diffusion equation has derivatives and thus applies to continuous quantities). A common model of discrete diffusion is the random walk. A random walk model is connected to the diffusion equation by considering an infinite number of random walkers starting from a non-uniform configuration, where the evolution of the concentration is described by the diffusion equation. Example of eight random walks in one dimension starting at 0. ...


The spreading of any quantity that can be described by the diffusion equation or a random walk model (e.g. momentum, ideas, price) can be called diffusion.


Diffusion is often important in systems experiencing an applied force. In a conducting material, the net motion of electrons in an electrical field quickly reaches a terminal velocity (resulting in a steady current described by Ohm's law) because of the thermal (diffusive) motions of atoms. The Einstein relation relates the diffusion coefficient to the mobility of particles. A voltage source, V, drives an electric current, I , through resistor, R, the three quantities obeying Ohms law: V = IR Ohms law states that, in an electrical circuit, the current passing through a conductor between two points is proportional to the potential difference (i. ... In physics, in kinetic theory the Einstein relation is a previously unexpected connection revealed by Einstein in his 1905 paper on Brownian motion: linking D, the Diffusion constant, and μ, the mobility of the particles; where k is Boltzmanns constant, and T is the absolute temperature. ...


In cell biology, diffusion is a main form of transport within cells and across cell membranes. This article or section includes a list of works cited or a list of external links, but its sources remain unclear because it lacks in-text citations. ...

Contents

Types of diffusion

Diffusion is the movement of particles from an area where their concentration is high to an area that always has low concentration.


Diffusion includes not only diffusion of particles, but transport phenomena occurring within thermodynamic systems under the influence of thermal fluctuations (i.e. under the influence of disorder; this excludes transport through a hydrodynamic flow, which is a macroscopic, ordered phenomenon), basically making both sides of the lipid bilayer of the same saturation of chemicals. Thermodynamics (Greek: thermos = heat and dynamic = change) is the physics of energy, heat, work, entropy and the spontaneity of processes. ... Hydrodynamics is fluid dynamics applied to liquids, such as water, alcohol, oil, and blood. ...


Diffusion is the process through which velocity thermodynamic system at local thermodynamic equilibrium returns to global thermodynamic equilibriums, through the homogenization of the values of its intensive parameters. Thermodynamics (Greek: thermos = heat and dynamic = change) is the physics of energy, heat, work, entropy and the spontaneity of processes. ... In thermodynamics, a thermodynamic system is said to be in thermodynamic equilibrium when it is in thermal equilibrium, mechanical equilibrium, and chemical equilibrium. ... intensive refers to an act that is done repetitively or with much force. ...

Atomic diffusion is a process whereby the random thermally-activated hopping of atoms in a solid results in the net transport of atoms. ... Three different views of Brownian motion, with 32 steps, 256 steps, and 2048 steps denoted by progressively lighter colors. ... Collective diffusion is the diffusion of a large number of particles, most often within a solvant Contrarly to brownian motion, which is the diffusion of a single particle, interactions between particles may have to be considered, unless the particles form an ideal mix with their solvant (ideal mix conditions correspond... Effusion can refer to: In literature, effusion is the process of opening the flood gates to ones emotions, so to speak. ... For other uses, see Electron (disambiguation). ... In electricity, current refers to electric current, which is the flow of electric charge. ... This article is in the process of being merged into Heat, and may be outdated. ... In mathematics — specifically, in stochastic analysis — an Itō diffusion is a solution to a specific type of stochastic differential equation. ... Knudsen diffusion is when the diffusivity is determined by the size of the containing vessel instead of the solvents or solutes. ... Momentum diffusion refers to the diffusion, or spread of momentum between particles of matter, usually in the liquid state. ... Hydrodynamics is fluid dynamics applied to liquids, such as water, alcohol, oil, and blood. ... Osmosis is the net movement of water across a partially permeable membrane from a region of high solvent potential to an area of low solvent potential, up a solute concentration gradient. ... Photon diffusion referes to a situation where photons travel through a material with a high optical depth and very short mean free path. ... Reverse diffusion referes to a situation where the transport of particles in a medium occurs towards regions of higher concentration, opposite to that observed during diffusion. ... According to the 2nd edition of the IUPAC Compendium of Chremical Terminology (1997), self-diffusion coefficient is the diffusion coefficient of species when the chemical potential gradient equals zero. ...

Diffusion displacement

The diffusion displacement can be described by the following formula

langle r_{k}^2 rangle=2cdot kcdot Dcdot t

where , k is the dimensions of the system and can be one, two or three. , D is the diffusion coefficient of the particles and , t is time. For the three-dimensional systems the above equation will be: The Diffusion Coefficient is given by where D is the diffusion coefficient in dimensions of [length2 time-1] T is the temperature in dimensions of Kelvin R is the gas constant in dimensions of [energy temperature-1 parts-1] See also Ficks law of diffusion Categories: Science stubs ... Look up time in Wiktionary, the free dictionary. ...

langle x^2 rangle + langle y^2 rangle + langle z^2 rangle = langle r_{3}^2 rangle = 6cdot Dcdot t

Isotope separation

-1...

Diffusion across biological membranes

such as dye in water it diffuses out to change the colour of water in a matter of seconds. An Experiment to Demonstrate Diffusion Requirements: facilitated difussion in cell membrane, showing ion channels and carrier proteins Facilitated diffusion (or facilitated transport) is a process of diffusion, a form of passive transport, where molecules diffuse across membranes, with the assistance of transport proteins. ... Ion channels are pore-forming proteins that help to establish and control the small voltage gradient that exists across the plasma membrane of all living cells (see cell potential) by allowing the flow of ions down their electrochemical gradient. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... The Respiratory System Among four-legged animals, the respiratory system generally includes tubes, such as the bronchi, used to carry air to the lungs, where gas exchange takes place. ... The alveoli (singular:alveolus), tiny hollow sacs which are continuous with the airways, are the sites of gas exchange with the blood. ... Subclasses & Infraclasses Subclass †Allotheria* Subclass Prototheria Subclass Theria Infraclass †Trituberculata Infraclass Metatheria Infraclass Eutheria Mammals (class Mammalia) are warm-blooded, vertebrate animals characterized by the production of milk in female mammary glands and by the presence of: hair, three middle ear bones used in hearing, and a neocortex region in... Human respiratory system The lungs flank the heart and great vessels in the chest cavity. ... General Name, Symbol, Number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, Period, Block 16, 2, p Appearance colorless (gas) very pale blue (liquid) Standard atomic weight 15. ... Carbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. ...

 1 wide glass tube 2 Corks Cotton wool soaked in ammonia solution 4 square sized red litmus paper 

Procedure: Cork the two ends of the wide glass tube. Plug the wet cotton wool with one of the corks and hang the litmus papers with a thread within the tube.


Observation: The red litmus papers turn blue.


Interpretation: The ammonia molecules by diffusion travels from higher concentration which is the cotton wool to lower concentration which is the rest of the glass tube.As the ammonia solution is alkaline, the red litmus papers turn blue. By changing the concentration of ammonia , the rate of color change of the litmus papers can be changed.


References

  1. ^ Biddle, Verne, and Gregory Parker. Chemistry: Precision and Design. Pensacola: A Beka Book, 2000. p109.

See also

Wikibooks
Wikibooks has more about this subject:
Constructing school science lab equipment/Apparatus for demonstrating osmosis
Look up Diffusion in
Wiktionary, the free dictionary.

Image File history File links Wikibooks-logo-en. ... Wikipedia does not have an article with this exact name. ... Wiktionary (a portmanteau of wiki and dictionary) is a multilingual, Web-based project to create a free content dictionary, available in over 150 languages. ... This article needs cleanup. ... Three different views of Brownian motion, with 32 steps, 256 steps, and 2048 steps denoted by progressively lighter colors. ... Collective diffusion is the diffusion of a large number of particles, most often within a solvant Contrarly to brownian motion, which is the diffusion of a single particle, interactions between particles may have to be considered, unless the particles form an ideal mix with their solvant (ideal mix conditions correspond... The heat equation or diffusion equation is an important partial differential equation which describes the variation of temperature in a given region over time. ... Diffusion equilibrium is reached when the concentrations of a diffusing substance in the two compartments becomes equal. ... Diffusion MRI is a specific Magnetic Resonace Imaging (MRI) modality that produces in vivo images of biological tissues weighted with the local microstructural characteristics of water diffusion. ... Ficks laws of diffusion describe diffusion and can be used to solve for the diffusion coefficient D. They were derived by Adolf Fick in the year 1855. ... Isotope separation is the process of concentrating specific isotopes of a chemical element by removing other isotopes, for example separating natural uranium into enriched uranium and depleted uranium. ... Mass transfer is the phrase commonly used in engineering for physical processes that involve molecular and convective transport of atoms and molecules within physical systems. ... Osmosis is the net movement of water across a partially permeable membrane from a region of high solvent potential to an area of low solvent potential, up a solute concentration gradient. ... The first edition of Transport Phenomena was published in 1960, two years after having been preliminarily published under the title Notes on Transport Phenomena based on mimeographed notes prepared for a chemical engineering course taught at the University of Wisconsin during the academic year 1957-1958. ... In the mathematical theory of stochastic processes, local time is a property of diffusions like Brownian motion. ...

External links


  Results from FactBites:
 
Diffusion (anthropology) - Wikipedia, the free encyclopedia (759 words)
The term diffusion is used in cultural anthropology to describe the spread of cultural items — such as ideas, styles, religions, technologies, etc. — between individuals, whether within a single culture or from one culture to another.
For example, the practice of agriculture is widely believed to have diffused from somewhere in the Middle East to all of Eurasia, less than 10,000 years ago, having been adopted by many pre-existing cultures.
Those disputed are fueled in part by the overuse of cultural diffusion, starting in the late 19th century, as a blanket explanation for all similarities between widely dispersed cultures.
  More results at FactBites »

 
 

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