Lecture Notes: Fick's Law

Introduction

Adolf Fick - Second most famous Adolf in history, known for contributions to science, especially his laws used in various scientific fields.
This lecture focuses on one of Fick's laws.

Imagine you are standing behind a blue-shaded wall in a box.
Small molecules are added to the front wall of the box.
Objective: Earn money (£5 per molecule) by having molecules pass from the front to the back wall in a set period (e.g., 1 hour).
Molecules are always in motion, not stationary.

Reduce Box Size: Move the back wall closer to minimize the distance molecules must travel.
Use Smaller Molecules: According to Graham's Law, smaller molecules diffuse faster.
Increase Molecule Count: Add more molecules to the front side to increase pressure and likelihood of passage.
Increase Surface Area: Widen the surface area of the walls to allow more molecules to pass through.

Traditional form of Fick's law:
- Flux (J) = -D * (dC/dx)
- D: Diffusion coefficient
- dC/dx: Concentration gradient
Factors influencing diffusion:
- Pressure (P): Higher the difference in pressure (ΔP) across walls, more molecules pass.
- Surface Area (A): Larger area increases the number of passing molecules.
- Diffusion Coefficient (D): Depends on properties like molecular size (Graham's Law) and solubility (Henry's Law).
- Thickness (T): Thicker walls decrease the rate of molecule passage.*

Flux (J): Rate of particle movement through a specific area.
Concentration Gradient (dC/dx): Change in concentration over a distance, influences diffusion rate.
Flow and Gradient: Flux = Gradient * D; showcases relationship and dependencies.*

Understand and apply Fick's Law to practical scenarios involving molecule diffusion.
Key takeaway: Diffusion rate is influenced by pressure difference, particle size, surface area, and wall thickness.