# What is the Difference Between Diffusion and Effusion

The main difference between diffusion and effusion is that diffusion is the movement of particles through a concentration gradient whereas effusion is the movement of gas molecules through tiny holes. Furthermore, diffusion describes the movement of solid, liquid, and gas molecules while only gases undergo effusion.

Diffusion and effusion are two methods used by different molecules to move from one to another place. Furthermore, Graham’s law describes the relationship between the rate of diffusion or effusion and the molar mass of gases.

### Key Areas Covered

1. What is Diffusion
– Definition, Driving Force, Efficiency
2. What is Effusion
– Definition, Driving Force, Efficiency
3. What are the Similarities Between Diffusion and Effusion
– Outline of Common Features
4. What is the Difference Between Diffusion and Effusion
– Comparison of Key Differences

### Key Terms

Concentration Gradient, Diffusion, Effusion, Gas, Liquids, Movement of Molecules, Solids

## What is Diffusion

Diffusion is a type of movement of molecules through a concentration gradient. It can occur in all three types of molecules including solids, liquids, and gases. The main importance of diffusion is that it allows the mixing of molecules with each other in the space in the absence of a barrier. However, it mainly occurs due to the concentration gradient of molecules. But, it depends on the size and the kinetic energy of molecules.

Figure 1: Diffusion

When considering gases, diffusion is the thermal random motion of molecules. Here, collisions that occur among gas molecules allows the release of molecular energy of the gas. Therefore, it becomes one of the major factors in reducing the efficiency of diffusion.

## What is Effusion

Effusion is a type of movement of gas molecules. It occurs with the escape of gas molecules through a pinhole into a vacuum. In simple terms, it describes the ability of gas molecules to move through a small opening. Here, the opening has to be smaller than the mean free path of the molecules.

Figure 2: Effusion

Furthermore, the concentration gradient of gas molecules between either side of the opening generates a pressure gradient across the opening. And, this pressure gradient serves as the major driving force which moves the gas molecules from the higher concentration of gases to a lower concentration through the opening.

## Similarities Between Diffusion and Effusion

• Diffusion and effusion are two mechanisms used by different types of molecules to move one to another place.
• Both methods occur through a concentration gradient.
• Moreover, the flow of molecules is constant and random.
• Besides, both do not use energy for the movement of molecules.

## Difference Between Diffusion and Effusion

### Definition

Diffusion refers to the net passive movement of particles (atoms, ions, or molecules) from a higher concentration region to a lower concentration region. Effusion refers to the movement of gas particles through a small hole. Thus, this is the main difference between diffusion and effusion.

### Type of Molecules

Another major difference between diffusion and effusion is that diffusion occurs in solid, liquid, and gas molecules while effusion occurs only in gas molecules.

### Type of Movement

Also, molecules move freely throughout space in diffusion while the movement of molecules occurs through tiny holes in effusion.

### Driving Force

Furthermore, the concentration gradient is the driving force in diffusion while the concentration gradient of gases generates a pressure gradient in effusion.

### Collision

One other difference between diffusion and effusion is that the collisions occur among the molecules in diffusion while there is no collision among the molecules in effusion.

### Efficiency

Moreover, diffusion is a less efficient method while effusion is more efficient due to the pressure difference involved in the process.

### Conclusion

Diffusion is the movement of molecules through a concentration gradient. Solid, liquid, and gas molecules use this method. On the other hand, the effusion is the movement of gas molecules through a concentration gradient, especially, through tiny holes. It is a highly efficient method due to the pressure gradient involved in the process. Therefore, the main difference between diffusion and effusion is the barrier which filters the gas.

##### References:

1. “Diffusion and Effusion|Boundless Chemistry.” Lumen Learning, Lumen, Available Here

##### Image Courtesy:

1. “Diffusion” By JrPol – Own work (CC BY 3.0) via Commons Wikimedia
2. “Effusion” By Astrang13 – Own work (CC BY-SA 3.0) via Commons Wikimedia