Difference Between Molecular Motion and Diffusion

Main Difference – Molecular Motion vs Diffusion

All matter is composed of particles. These particles can be atoms, ions or molecules. Most of the times, substances composed of molecules can be found because atoms or ions alone are not stable. These molecules are in constant motion. Matter can exist primarily in three main physical states. They are solid state, liquid state, and gaseous state. Molecules in all these states of matter are in motion inside the substance. Molecular motion and diffusion are two types of motion of molecules in a substance. The main difference between molecular motion and diffusion is that molecular motion is the movement of molecules in a substance here and there without any external influence whereas diffusion is the movement of molecules from a high concentrated region to a low concentration region.

Key Areas Covered

1. What is Molecular Motion
      – Definition, Explanation of Mechanism
2. What is Diffusion
      – Definition, Explanation of Mechanism
3. What is the Difference Between Molecular Motion and Diffusion
      – Comparison of Key Differences

Key Terms: Diffusion, Molecular Motion, Molecules, Particles

What is Molecular Motion

Molecular motion is the random movement of molecules in a substance without any applied external influence. In other words, it is the movement of molecules here and there inside the boundary of a substance. This motion of molecules causes molecular collisions. These collisions cause the molecules to bounce on each other.

Figure 1: Motion of Molecules in the Different States of Matter

Molecules that build up matter is always in constant motion. But the nature of this motion is different from each other in three states of matter. In solid substances, the molecules are tightly packed. Therefore, molecules in solid materials exhibit minimum motion. But in gaseous compounds, the molecules can move freely because there is no packing of molecules in gases. In liquid matter, molecules observe a limited but considerable motion when compared to solids.

When an external influence is generated, the motion of molecules can be changed. For example, when the temperature of a gas is increased, the internal energy of the gaseous compound increases, resulting in a high kinetic energy. Then the molecules begin to move faster than before. Similarly, when pressure is applied to a gas, the gas tends to be compressed. Then the volume that is available for gas molecules to move is decreased. As a result, the movement is limited.

What is Diffusion

Diffusion is the movement of molecules from a region of high concentration to a region of low concentration. In other words, the molecules move through a concentration gradient. Therefore, the factors that affect the concentration gradient will affect the diffusion.

The diffusion occurs until the concentration of the whole system becomes equal at every point. In other words, diffusion occurs until the amount of molecules in the low concentration region and the high concentration region becomes equal. Molecules spread everywhere evenly in a solution through diffusion.

Figure 2: Diffusion of Molecules through Semi-Permeable Barrier

Diffusion of molecules in a solution can be monitored using small strategies. For example, impermeable barriers totally block the movement of molecules. Semi-permeable barriers block some molecules from moving to a certain region, but it allows some selected molecules to pass through.

Difference Between Molecular Motion and Diffusion

Definition

Molecular Motion: Molecular motion is the random movement of molecules in a substance without any applied external influence.

Diffusion: Diffusion is the movement of molecules from a high concentration region to a low concentration region.

Nature of Motion

Molecular Motion: Molecular motion is random.

Diffusion: Diffusion always occurs through a concentration gradient.

External Factors

Molecular Motion: Molecular motion is affected by external factors such as temperature and pressure.

Diffusion: Diffusion is affected by factors that affect the concentration gradient.

Final Stage

Molecular Motion: Molecular motion cannot be predicted due to molecular collisions. Thus the there is no final stage since molecules are always in random motion.

Diffusion: After diffusion, a solution with uniformly distributed solutes is created.

Conclusion

Molecules in substances are always in constant but random motion. Therefore, these molecules colloid with each other bouncing themselves. This is known as molecular motion. Diffusion is also a type of molecular motion. But there are differences between these two concepts. The main difference between molecular motion and diffusion is that molecular motion is the movement of molecules in a substance here and there without any external influence whereas diffusion is the movement of molecules from a highly concentrated region to a lowly concentration region.

References:

1. “Diffusion.” Wikipedia, Wikimedia Foundation, 25 Sept. 2017, Available here. Accessed 2 Oct. 2017.
2. “Motion of Molecules”. New York University,  Available here. Accessed 2 Oct. 2017.
3. “Molecular Motion and Diffusion Lecture Notes – Biology 10.” Google Sites, Available here. Accessed 2 Oct. 2017.

Image Courtesy:

1. “Solid-liquid-gas” By Solid-liquid-gas.jpg: Sadi Carnotderivative work: Dave.Dunford (talk) 13:43, 15 December 2010 (UTC) – Solid-liquid-gas.jpg (Public Domain) via Commons Wikimedia
2. “Diffusion.en” By Diffusion.en.jpg: derivative work: Quasar Jarosz (talk) – Diffusion.en.jpg (Public Domain) via 

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