Difference Between Effusion and Diffusion

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Effusion Definition Chemistry

In chemistry, diffusion and effusion are one of the most commonly used terms. However, they are nothing but two varying properties of the gases. When you study these terms, it can get quite confusing if you are just starting to study the gases. Both diffusion and effusion may sound quite similar to you, but they are two entirely different terms. Both of them mean different things and hence we cannot use them interchangeably. In this article, we will study about the diffusion and effusion definition chemistry, the diffusion and effusion meaning, and take a look at the difference between diffusion and effusion. Let us first learn about both the terms in detail.

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What are Effusion and Diffusion?

Diffusion refers to the ability of the gases to mix without needing a bulkier motion. On the other hand, effusion refers to the ability of the gases for travelling or escaping through a tiny hole having a smaller aperture and from a place having a higher concentration to a lower concentration.

However, both diffusion and effusion are the processes occurring in our day-to-day lives. Diffusion generally occurs inside our body in which exchanges of oxygen, nutrients and energy takes place within our body. We need to know what is the difference between diffusion and effusion chemistry.

The primary difference between the effusion and diffusion is the barrier which tends to either exist or be absent whenever a specific volume of gas tends to move from one place to another. However, let us take a look at the differences between diffusion and effusion.

Difference Between Diffusion and Effusion



Effusion happens when the gaseous molecules tend to escape through the pinhole into the vacuum.

During the process of diffusion, one gas tends to mix with the other generally by thermal random motion which results in the collision between each of the gases while it releases molecular energy.

Effusion refers to the ability of the gas to travel through a tiny opening.

Diffusion refers to the ability of the gases to mix, generally when there is an absence of a barrier.

Effusion tends to occur when the aperture or size of the hole is much smaller when compared to the mean free path of the constituent molecules.

Diffusion tends to occur when there are no holes present or when the holes in the barrier are much larger when compared to the mean free path.

During the process of effusion, the particles tend to move faster than diffusion since there is no collision occurring between the molecules.

The rate of diffusion is limited and depends on the size and the kinetic energy of the other particles.

Effusion happens or is facilitated when there is a difference in pressure.

Diffusion happens because of the difference in the concentrations.

FAQ (Frequently Asked Questions)

Q1. What are the Definitions of Diffusion and Effusion?

Ans: The definitions of diffusion and effusion are as follows.

Diffusion: Diffusion is known as the process of the particles that tend to move from an area of higher concentration to an area of lower concentration. The rate of this diffusion movement is a function of the size of the particles, viscosity of the medium and temperature. Diffusion tends to result in the gradual mixing of the materials and later tends to form a homogeneous mixture.

Effusion: It is not just that the gaseous molecules tend to move with higher kinetic energy. It is their smaller size that enables them to move through the small and tiny openings too. This process is known as the process of effusion. If effusion has to occur, the diameter of the holes should be smaller than the mean path of the molecules. Also, the opening of the hole should be smaller than the molecule’s mean free path. Otherwise, the gaseous molecule would only move back and forth in the hole. We can define effusion as the continuous random motion of the particles. Over some time, this random motion would result in the passing of some of the molecules through the hole.

Q2. What is Graham’s Law of Diffusion and Effusion?

Ans: According to Graham Law, the rate of the effusion or diffusion of the gas tends to be inversely proportional to the root of its total molecular weight. Hence, if the total molecular weight of a gas is four times higher than that of another gas, it can easily diffuse through the porous membrane. It can even escape through the tiny pinhole of a vessel and at half of the rate than that of the other. It is essential to note that the heavier gases tend to diffuse at a slower rate. The complete theoretical explanation of this law was shown many years later with the help of the kinetic theory of gases. Graham’s Law provides us with a basis to separate the isotopes with the help of diffusion. This method had a very crucial role in developing the atom bomb.