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Diffusion in Solids, Liquids, and Gases

  • Last Updated : 20 Nov, 2021

While the meal is being cooked in the kitchen, people may smell the food while sitting in the drawing-room. Because of diffusion in the air, the vapour from the food reaches us and gives us the fragrance of food. People can smell a burning incense stick from a distance. When they burn an incense stick, the incense inside it vaporizes due to the heat. The vapour from the incense stick interacts with the air and makes its way to us. 

Because of diffusion, when sugar is introduced to water, it is combined. Because of their constant movement, sugar particles collide with water particles. Carbonated drinks are made by allowing gas to diffuse through water. When the cap of a carbonated drink bottle is opened, we hear a hissing sound, which is caused by dispersed gas escaping from the water. Aquatic animals breathe dissolved oxygen in the water. Because of the dissolved carbon dioxide in water, aquatic plants generate their food underwater. Diffusion caused these gases to dissolve in water.

What is Diffusion?

Diffusion is the spreading out or mixing of a substance with another substance caused by the motion of its particles. The process of one substance diffusing into another continues until a homogeneous mixture is achieved.

Diffusion is a feature of matter that is determined by the movement of its particles. Diffusion is a phenomenon that occurs in gases, liquids, and solids.

As the temperature of the dispersing substance rises, so does the rate of diffusion. In gases, diffusion is the fastest, whereas in solids, it is the slowest. Various gases have different diffusion rates. Denser gases intermingle at a slower rate than lighter gases. Dissemination occurs in both liquids and solids. The pace of diffusion in solids, on the other hand, is quite slow. Diffusion in liquids is slower than diffusion in gases because liquid particles travel slowly.

Factors Affecting Diffusion are-

  • Density: The rate of diffusion is proportional to the mass of the liquid or gas being diffused. The lower the rate of diffusion, the higher the density.
  • Temperature: The temperature has a direct relationship with the rate of diffusion. The kinetic energy of the constituent units increases as the temperature rises, and they travel faster, resulting in an enhanced rate of diffusion.

Rate of Diffusion 

The rate of diffusion increases as the temperature rises and decreases as the temperature falls. As the temperature rises, so does the kinetic energy, which accelerates the movement of matter particles. The rate of diffusion increases as the speed of movement increases.

For example, people can smell cold food from a short distance, whereas we can smell hot food from a long distance. Because the kinetic energy of the smell coming out of the cold food in the form of gas is insufficient to traverse a greater distance. When food is hot, however, the vapour that escapes moves faster due to the increased kinetic energy and reaches us even if we are far away. 

Diffusion in Gases

Gases have a very fast diffusion rate. Because gas particles move very swiftly in all directions. The rate of diffusion of a gas, on the other hand, is determined by its density. The diffusion of light gases is faster than that of heavy gases because gas particles have higher kinetic energy, they move at a faster rate. Because of the high-speed movement of particles, gas diffuses quickly.


  1. Only near the mouths of chimneys can one observe smoke flowing from industries. It mixes with the air after climbing to a high altitude.
  2. When someone ignites an incense stick in a corner of any room, the scent soon travels around the room due to the smoke’s diffusion into the air.

Diffusion in liquids

Liquid diffusion is slower than gas diffusion. This is due to the fact that liquid particles travel more slowly than gas particles. Because of kinetic energy, the liquid particles have enough mobility to allow diffusion. Diffusion causes two liquids to combine when they are kept together.


  1. The diffusion of potassium-permanganate(chemical used in the treatment of skin infection\burns) particles into water, for example, causes the purple colour of potassium-permanganate to diffuse into the water.
  2. Aquatic plants use dissolved carbon dioxide to prepare food through photosynthesis, whereas aquatic animals breathe using dissolved oxygen in the water. This is an illustration of gas diffusion into a liquid.

Diffusion in solids:

Diffusion can happen in solids as well. Solid-state diffusion is an extremely slow process. Solid particles have the lowest kinetic energy and so do not move. As a result, in the case of solids, diffusion takes a lengthy time.


  1. While writing something on a blackboard and then leaving it filthy for an extended length of time, cleaning the blackboard becomes pretty tough. This is owing to the fact that certain chalk particles have spread into the blackboard surface.
  2. Alloys are metal alloys made up of two or more metals. Because of the diffusion of solid into solid, alloys can be formed. Alloys include bronze, steel, and brass.

Sample Questions

Question 1: What is the importance of gas diffusion in water? Explain with example.


Diffusion is the process by which molecules shift from a high-concentration region to a low-concentration zone. Diffusion differs from osmosis in that osmosis primarily involves the flow of water, whereas diffusion mostly involves the movement of particles via a membrane.

Example: The oxygen from the air we breathe diffuses from the lungs to the bloodstream as we breathe in. The oxygen that was breathed in a gaseous state is now combined in the bloodstream as a liquid. As a result, one of the most important phenomena is gas diffusion in liquid (oxygen gas from our lungs to the bloodstream).

Question 2: What does the “random walk” of particles refers to in diffusion?


Brownian motion, often known as “random walk,” describes how molecules travel through space, bouncing off other particles and obstacles and reacting with their surroundings.

Question 3: When does the concentration gradient no longer exist?


It is considered to have reached equilibrium when the molecules that have been introduced to a substance have distributed throughout the substance. The concentration of molecules in the substance is now uniform throughout, and the gradient has vanished.

Question 4: Why are the diffusion rate differs between gases, liquids, and solids?


The distance between molecules is a key difference between these various types. Molecules in gases are more widely spaced than in liquids or solids. Because diffusion involves molecular collisions, the distance between them is an essential component.

Question 5: Why do molecules appear to move down a concentration gradient as they diffuse through a substance?


Diffusion is the movement of molecules through a medium due to their random motion and collisions with other particles. Molecules will shift from a high-concentration location to a low-concentration area over time, becoming uniformly disseminated throughout.

Question 6: Explain why Osmosis is different from diffusion.


Osmosis is a kind of diffusion in which two liquid solutions are separated by an SPM. The SPM is unable to pass through solutes. Because the dilute solution contains more solvent particles than the concentrated solution, these particles migrate through SPM from the former to the latter.

Question 7: Why Interstitial diffusion is generally faster than diffusion by vacancy mode?


The likelihood of a neighbouring interstitial site forming is substantially higher than that of a vacancy under normal conditions. Furthermore, the interstitial atoms’ bonds to the host lattice are substantially weaker.

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