Question

Molecular diffusion in gases is fastest when the:

• A. Temperature is low
• B. Pressure is high
• C. Molecular weight is high
• D. Temperature is high

Hint:

Logic Tip: Diffusion is just molecules bumping their way through a crowd. To get through the crowd the fastest, you want the molecules to be highly energetic (High Temperature) and the crowd to be very thin (Low Pressure).

Answer 1

The Correct Option is D

Concept:
Molecular diffusion in gases relies entirely on the random thermal motion of molecules (Brownian motion). The speed of diffusion is dictated by how fast the molecules are moving and how freely they can travel before hitting each other.

Step 1: Temperature is a direct measure of the average kinetic energy of the gas molecules. At high temperatures, molecules move much faster, leading to much more rapid diffusion.

Step 2: High pressure means gas molecules are packed tightly together. This decreases the "mean free path" (the distance a molecule can travel before colliding with another), which significantly slows down diffusion.

Step 3: Heavier molecules (high molecular weight) move more sluggishly than lighter molecules at the same temperature (Graham's Law), resulting in slower diffusion.

Step 4: To achieve the fastest possible diffusion, you need light molecules moving very fast in an uncrowded space. Therefore, High Temperature (and low pressure/low molecular weight) creates the fastest diffusion.