Molecular diffusion

（重定向自Simple diffusion）

Diffusion from a microscopic and macroscopic point of view. Initially, there are solute molecules on the left side of a barrier (purple line) and none on the right. The barrier is removed, and the solute diffuses to fill the whole container. Top: A single molecule moves around randomly. Middle: With more molecules, there is a clear trend where the solute fills the container more and more uniformly. Bottom: With an enormous number of solute molecules, all randomness is gone: The solute appears to move smoothly and systematically from high-concentration areas to low-concentration areas, following Fick's laws.

Schematic representation of mixing of two substances by diffusion

Illustration of low entropy (top) and high entropy (bottom)

Molecular diffusion, often simply called diffusion, is the thermal motion of all (liquid or gas) particles at temperatures above absolute zero. The rate of this movement is a function of temperature, viscosity of the fluid and the size (mass) of the particles. Diffusion explains the net flux of molecules from a region of higher concentration to one of lower concentration. Once the concentrations are equal the molecules continue to move, but since there is no concentration gradient the process of molecular diffusion has ceased and is instead governed by the process of self-diffusion, originating from the random motion of the molecules. The result of diffusion is a gradual mixing of material such that the distribution of molecules is uniform. Since the molecules are still in motion, but an equilibrium has been established, the end result of molecular diffusion is called a "dynamic equilibrium". In a phase with uniform temperature, absent external net forces acting on the particles, the diffusion process will eventually result in complete mixing.

单词	Simple diffusion
释义	Simple diffusion 原声例句 Crash Course 解剖生理学篇 So, the principles that make respiration possible are relatively simple — diffusion and bulk flow. 因此，使呼吸成为可能的原理是相对简单的——扩散和容积运动。 Crash Course 解剖生理学篇 Instead, you get all of your oxygen the way that your oldest, smallest evolutionary ancestors did — by simple diffusion. 取而代之的是，你会像你最古老、最小的进化祖先一样——通过简单的扩散来获得所有的氧气。 Crash Course 解剖生理学篇 That's why your respiratory system is the way it is: It's set up to take full advantage of both bulk flow and simple diffusion. 这就是为什么你的呼吸系统是这样的：它的设置充分利用了容积运动和简单扩散。 Crash Course 解剖生理学篇 It's only by working together and using both the bulk flow and simple diffusion of oxygen that they can make possible the process of cellular respiration. 只有通过协同工作，同时利用容积运动和氧气的简单扩散，它们才能使细胞呼吸的过程成为可能。科学杂志：科技 The bots were able to deliver their cargo to the right place in much less time than simple diffusion would allow. 机器人能够在比简单扩散所允许的时间短得多的时间内将货物运送到正确的地方。 Crash Course 解剖生理学篇 And they did it through simple diffusion — when a material automatically flows from where it is concentrated, to where it is less concentrated, so it balances out. 它们通过简单的扩散实现了这一点——当一种物质自动从它集中的地方流向它不那么集中的地方，因此它获得了平衡。 Crash Course 解剖生理学篇 But today you learned how it does work — including the mechanics of both simple diffusion and bulk flow, and the physiology of breathing, and the anatomy of the conducting zone, and the respiratory zone, of your respiratory system. 但是今天你们学到了它是如何工作的——包括简单扩散和整体流动的机制，呼吸的生理学，以及你呼吸系统的传导区和呼吸区的解剖学。英语百科 Molecular diffusion （重定向自Simple diffusion） Molecular diffusion, often simply called diffusion, is the thermal motion of all (liquid or gas) particles at temperatures above absolute zero. The rate of this movement is a function of temperature, viscosity of the fluid and the size (mass) of the particles. Diffusion explains the net flux of molecules from a region of higher concentration to one of lower concentration. Once the concentrations are equal the molecules continue to move, but since there is no concentration gradient the process of molecular diffusion has ceased and is instead governed by the process of self-diffusion, originating from the random motion of the molecules. The result of diffusion is a gradual mixing of material such that the distribution of molecules is uniform. Since the molecules are still in motion, but an equilibrium has been established, the end result of molecular diffusion is called a "dynamic equilibrium". In a phase with uniform temperature, absent external net forces acting on the particles, the diffusion process will eventually result in complete mixing.
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