Dhristi JEE 2022-24

What is the Brownian Motion?

"Brownian motion in chemistry is a random movement. It can also be displayed by the smaller particles that are suspended in fluids. And, commonly, it can be referred to as ``Brownian movement"- the Brownian motion results from the particle's collisions with the other fast-moving particles present in the fluid.


When two particles collide, the path of one particle will be changed. A further collision also causes the particle to follow a random motion, which is called zigzagging. Momentum and energy are exchanged between the particles during this process.


An illustration that describes the random movement of the fluid particles can be given as follows.


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Note: The Brownian motion was named after the Scottish Botanist Robert Brown, who first observed that when placed in water, pollen grains move in random directions.


Brownian Movement

Biologically the Brownian Movement occurs when a particle moves randomly in a zigzag pattern, which can be observed under a high-power microscope. A similar motion is described by Robert Brown as the Brownian movement and resembles how pollen grains move in the water.


The Brownian movement of pollen was later clarified by Albert Einstein in his paper, explaining that the pollen was moved by water molecules. Molecular and atomic existence has been strengthened with this discovery.


Modern atomic theory is based on the Brownian movement, which is imperative to comprehend. Also, the kinetic theory of gasses is based on the Brownian motion model of particles. The mathematical models that describe Brownian motion are used in various disciplines such as Physics, Maths, Economics, Chemistry, and more.


What is the Brownian Movement in Chemistry?

The Brownian movement in chemistry, which is also called Brownian motion, can be defined as the erratic or uncontrolled movement of particles in fluid because of their constant collision with other fast-moving molecules.


In general, this random movement of a particle can be observed to be stronger in the less viscous liquid, smaller sized particles, and at a higher temperature. There also exist other factors that affect the movement of particles in a fluid.


One of such most common examples of the Brownian motion can be given as diffusion. The cases where calcium is diffused in bones or pollutants are diffused in the air can be considered examples of this effect.


Brownian Movement in Colloids

We can see the Brownian motion effect in all types of colloidal sol. On the other hand, this phenomenon explains the sol particles' random motion clearly and indicates that these particles are not static. Nevertheless, the major reason for this type of motion in the sol particles is the unequal bombardment of the depressed phase particle, leading to a non-uniform movement in native because of the particle's size difference.


Meanwhile, the Brownian movement cannot be seen in the true solution because it is homogeneous, and there lies a uniform bombardment. However, considering colloids, the system is heterogeneous, and the bombardments are non-uniform, leading to a random measurement.


One of the major advantages of this effect is that it keeps the sol particles in continuous motion so the particles do not settle at the bottom by further preventing the lyophobic sols' coagulation. So, this type of motion increases the stability of a sol. Brownian motion can also be observed in the cell's plasma, where the particles in the cell also exist in random motion without making the plasma in the cell dry.


Cause of Brownian Motion

The primary causes of the Brownian Motion can be listed as follows:

  • The particle's size is inversely proportional to the motion's speed, which means the small particles exhibit faster movements.

  • This is due to the momentum transfer being inversely proportional to the particles' mass. At the same time, lighter particles obtain greater speeds from collisions.

  • The Brownian motion's speed is inversely proportional to the viscosity of the fluid: the lower the fluid's viscosity, the faster the Brownian movement.

  • Viscosity can be given as a quantity that expresses the internal friction magnitude in a liquid. It is the resistance’s measure for a fluid's flow.


Effects of Brownian Motion

  • The Brownian movement causes fluid particles to be in constant motion.

  • This prevents the particles from settling down, leading to the colloidal sol's stability.

  • We can distinguish a true sol from a colloid with the help of this motion.

Albert Einstein's paper on Brownian motion provides significant evidence that molecules and atoms exist. In the kinetic theory of gases, the particles of the Brownian motion model are responsible for describing temperature, volume, and pressure.

FAQs (Frequently Asked Questions)

1. What is an example of brownian motion?

Brownian Motion Examples: Brownian motion is primarily observed in transport systems that are affected by large currents and exhibit pedesis at the same time. For example, the motion of pollen grains on a still body of water. Diffusion of pollutants in the air is caused by dust particles moving in a room- usually caused by air currents.

2. How is brownian motion caused?

Brownian motion occurs when particles collide with surrounding molecules, causing them to move randomly. An induced diffusion of particles occurs when a concentration gradient induces the movement of particles. This movement occurs when particles are shifted from high to low concentrations.

3. How does brownian motion work in gas?

Regardless of whether a substance is liquid or gas (collectively called fluid), particles move randomly. Brownian motion is responsible for this. In fluids, moving particles bombard these particles, causing them to behave in this manner. Larger particles can be moved by molecules that move quickly.

4. Why does the real solution not follow the brownian movement?

True solutions contain smaller, homogeneous solute particles. These particles move uniformly and do not show Brownian motion.

5. What is the role of the brownian movement in maintaining the stability of the sols?

Collisions between water molecules and colloidal particles result in this phenomenon. Brownian motion is responsible for this stirring effect. As a result, the particles do not settle down. Thus, it prevents the sol particles from settling down, which has an impact on its stability.

6. What causes brownian movement in a colloidal solution?

Colloidal “solutions” consist of minute particles (solid or liquid) which cannot be seen by the naked eye but can be seen through a microscope, suspended in a liquid medium (solvent). They are not true solutions. For example, milk. Milk consists of minute fat particles suspended in water. The fat particles scatter light and can be seen. Now the question is why milk appears to be “milky”? (opaque and white) and not like water? So, you can observe Brownian motion when the fat particles are kicked here and there by the water molecules.

7. What is the difference between brownian motion and motility?

It can be quite complex to differentiate between a movement due to Brownian motion and movement due to other effects. In biology, for example, an observer needs to be able to tell whether a specimen is moving because it is motile (capable of movement on its own, perhaps due to cilia or flagella) or because it is subject to Brownian motion. Typically, it's imaginable to segregate the processes because Brownian motion appears jerky, random, or like a vibration. True motility appears often as a path, or else the motion is twisting or turning in a specific direction. In microbiology, motility can be established if a culture inoculated in a semisolid medium wanders away from a stab line.

8. How does the brownian motion affect temperature?

Let us discuss the cause of the Brownian movement. Indeed, the temperature is what we feel at the macroscopic (otherwise human) scale, which is caused by the Brownian motion at the microscopic or molecular scale.


The more energetic the molecule's Brownian motion, the higher the temperature we sense. Absolute temperature is proportional to Brownian motion's kinetic energy per unit mass in a more specific way.


So, if we raise the temperature, the Brownian motion becomes more energetic.

9. How come the uniform electric field gives a zig-zag motion to the electron present in the wire?

In any of the non-superconducting conductors having a potential difference over its endpoints, the band electrons of mobile conduction move towards a more positive potential (via conventional current flow in the opposite direction). Not only are all these electrons affected by the potential difference across the wire, but also they are affected by all the charged particles present in the conductor.


While the other charged particles are also in motion (some more so than others). So, the resultant effect is for the conduction band's electrons to have some random amount (or "zig-zag") motion in addition to their movement from one conductor end to another. The average distance traveled by a single electron is greater than the length of a physical conductor.

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