Let's Start with the fact that the liquid is an intermediate aggregate state. At the critical point of boiling it is similar to gases, and at low temperatures are the characteristics similar the solid. The liquid had no ideal model, which significantly complicates the description of its equilibrium thermodynamic properties, freezing point, viscosity, diffusion, thermal conductivity, surface tension, entropy, enthalpy.
What is diffusion? It's spreading, spreading, the movement of the particles of the medium, which leads to the transfer of a substance, establish equilibrium concentrations. In the absence of external influences the process determined by the thermal motion of the particles. In this case, the diffusion process associated with the concentration directly proportional. The diffusion flux will change similarly to the concentration gradient.
If the diffusion in the liquid occurs at the temperature change, called thermal diffusion, electric field – electrodiffusive.
The motion of larger particles in the liquid or gas occurs under the laws of Brownian motion.
Diffusion in gases, liquids and solids flows at different speeds. Because of differences in the character of the thermal motion of particles in different environments, the maximum speed the process is in gases, and the lowest figure - in solids.
The Trajectory of the particle is a broken line as periodically changing direction and speed. Because of the disorder of the movement there is a gradual removal of the particles from the original position. Offset it in a straight line much shorter than the path that takes place in a broken trajectory.
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Diffusion in a fluid is subject to two laws of Fick:
Diffusion in liquids is characterized by jumps of the molecules from one equilibrium position to another. Each such jump is observed in the case of the communication energy of the molecule in an amount sufficient to break the connection with other particles. Average jump does not exceed the distance between the molecules.
Arguing over what is diffusion in liquids, we note that the process depends on the temperature. With its increase occurs "loosening" of the structure of the liquid, resulting in a sharp increase in the number of hopping capability per unit time.
Diffusion in gases, liquids and solids has some distinctive characteristics. For example, in solids the mechanism is associated with the movement of atoms within the crystal lattice.
Diffusion in liquids is of practical interest due to the fact that it is accompanied by a leveling of concentration of the substance in the initially heterogeneous environment. With sites having a greater concentration of particles can take substantially longer.
Experiments with liquids showed that the diffusion is of particular importance in chemical kinetics. During the course of the chemical process on the surface of the reactants or catalyst of this process contributes to the determination of the speed of withdrawal of the reaction products and the addition of the initial reagents.
What accounts for diffusion in liquids? Solvent molecules are able to penetrate through the translucent membrane, resulting in osmotic pressure. This phenomenon has found application in the chemical and physical methods of separation of substances.
In this case, the diffusion model can be seen on the example receipt in the lungs oxygen of the air, absorption from the intestine into the blood products of digestion, absorption by root hairs mineral elements. Diffusion of ions occurs during the generation of muscle and nerve cells bioelectric impulses.
Physical factor that affects the selectivity of accumulation in the cells of the body of certain elements varies the rate of penetration of ions through the cell membrane. This process can be expressed by Fick's law, replacing the value of the diffusion coefficient increased permeability of the membrane and the concentration gradient to use the difference between the values on both sides of the membrane. In the diffusive penetration of water and gases into the cell, changing the osmotic pressure outside and inside the cell.
By Analyzing what determines the diffusion, we note that there are several types of this process. A simple form is associated with the free transport of ions and molecules in the direction of the gradient of their electrochemical potential. For example, this option is suitable for those substances whose molecules have negligible size, for example, methyl alcohol, water.
A Limited version implies the weak transfer agent. For example, the cell is not able to penetrate even small-size particles.
Diffusion was opened during the heyday of the ancient Greek culture. Democritus and Anaxagor were convinced that any substance consists of atoms. A variety of substances common in nature, they explain the connections between individual atoms. They assumed that these particles can be mixed, forming new substances. Among the founders of molecular-kinetic theory which explained the mechanism of occurrence of diffusion, a special role was played by Mikhail Lomonosov. They were given the definition of the molecule, the atom, explained the mechanism of dissolution.
Experience with sugar allows you to understand all the features of the diffusion process. If iced tea put a piece of sugar, gradually at the bottom of the Cup forms a thick syrup. It is visible to the naked eye. After some time the syrup is evenly distributed throughout the volume of the liquid and no longer be visible. This process takes place spontaneously and does not involve the mixing of the components of the solution. Similarly, the spread for an entire room of perfume.
The experiments show that diffusion is a spontaneous process of penetration of molecules of one substance into another. Spreading occurs in all directions, despite the presence of gravity. This is a direct confirmation of the constant movement of molecules of a substance.
So, in the above example is diffusion of sugar molecules and water, which is accompanied by uniform distribution of molecules of organic substances throughout the fluid volume.
Experiments allow to detect the diffusion, not only in liquids but also in gaseous substances. For example, you can set on the scales a container of pairs of the ether. Gradually, the Cup will come to equilibrium, then a glass of air will be heavier. What causes this phenomenon?
Over time the molecules of air are mixed with particles of air, and the room begins to feel a specific smell. In the course of physics of high school is considered an experiment in which the teacher dissolves a grain of potassium permanganate (potassium permanganate) in water. First, we clearly see the trajectory of the grains, but gradually the whole solution becomes a uniform color. Based on the conducted experiment, the teacher explains the features of the diffusion.
To identify factors that affect the speed of process liquids you can use water of different temperatures. In hot liquids the process of mutual agitation of the molecules is much faster, hence, there is a direct relationship between the temperature value and the flow rate of diffusion.
The Experiments conducted with gases, liquids and solids, it is possible to formulate the laws of physics, to establish the relationship between the individual values.
It is the result of the experiments was the mechanism of mutual penetration of particles of one substance into another, it proves the randomness of their movement. Empirically it was found that the fastest diffusion occurs in gaseous substances. This process is of great importance for wildlife, used in science and technology.
Due to this phenomenon is supported by the homogeneous composition of the earth's atmosphere. Otherwise there would have been a stratification of the troposphere on a separate gaseous substances, and the heavy carbonic acid gas, unfit for respiration, would be closest to the surface of our planet. What good would it do? Wildlife simply ceased to exist.
The role of diffusion and in the plant world. The magnificent crown of trees can be explained by diffusion exchange across the surface of the leaves. The result is not only breathing, but also the nutrition. Currently in agriculture used foliar feeding of shrubs and trees, involving the spraying of the crowns of special chemical compounds.
It is with the diffusion of the plant from the soil receives nutrients...
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