Difference Between Molecular Motion and Diffusion l Molecular Motion vs Diffusion


The key difference between molecular motion and diffusion is that the molecular motion is the movement of molecules inside a substance without any external influence whereas diffusion is the movement of molecules from a region of high concentration to a region of lower concentration.

Molecular motion and diffusion are very important as explanations for the behavior of molecules of substances. All matter contains particles; atoms, ions or molecules. most of the times, we can find molecules instead of atoms or ions because molecules are more stable. Moreover, all forms of matter are always in one of three states of matter; gas, liquid or solid state. The movement of the molecules in these three states are described by molecular motion and diffusion.

CONTENTS

1. Overview and Key Difference
2. What is Molecular Motion
3. What is Diffusion
4. Side by Side Comparison – Molecular Motion vs Diffusion in Tabular Form
5. Summary

What is Molecular Motion?

Molecular motion is the movement of molecules inside a substance without any external influence. This means it is the movement of particles inside a substance here and there randomly. This movement occurs only inside the boundary of the substance. These movements cause molecular collisions, in which molecules colloid with each other. These collisions cause the bouncing of molecules.

Since the molecules of a solid are well-packed, the molecular motions in the solids are very limited. But in liquids, there are more movements and collisions when compared with solids. In gases, molecules have a large space for molecular movement and also there is a high degree of collisions. If we use an external influence on a substance, the movements change accordingly. Ex: If we increase the temperature of a gas, the speed of movement increases, thus the collisions are also high.

What is Diffusion?

Diffusion is the movement of molecules from a region of high concentration to a low concentration via a concentration gradient. These movements occur in the same solution. The factors that affect the concentration gradient affects the diffusion as well.

Difference Between Molecular Motion and Diffusion l Molecular Motion vs Diffusion

Figure 01: Diffusion in a Simple Diagram

This motion terminates when the concentrations of the two regions become equal at every point. This means this motion occurs until the concentration gradient disappears. Then the molecules spread everywhere inside the solution.

What is the Difference Between Molecular Motion and Diffusion?

Molecular motion is the movement of molecules inside a substance without any external influence. It is a random motion. In addition, external factors can affect this motion, i.e. temperature and pressure. Diffusion is the movement of molecules from a region of high concentration to a low concentration via a concentration gradient. Therefore, it is not a random motion. The factors affecting the concentration gradient affects the motion of molecules. This is the main difference between molecular motion and diffusion.

Difference Between Molecular Motion and Diffusion l Molecular Motion vs Diffusion

Summary – Molecular Motion vs Diffusion

Molecular motions and diffusion are very important in explaining the behavior of particles inside substances. The difference between molecular motion and diffusion is that the molecular motion is the movement of molecules inside a substance without any external influence whereas diffusion is the movement of molecules from a region of high concentration to a region of lower concentration.

Reference:

1. “Motion of Molecules (Grades 6-8).” NYU. Available here  
2. “Diffusion.” Wikipedia, Wikimedia Foundation, 27 June 2018. Available here 

Image Courtesy:

1.’Diffusion’ By JrPol – Own work, (CC BY 3.0) via Commons Wikimedia