State that the energy for diffusion comes from the kinetic energy of molecules and ions.

3.1 Diffusion

Objective: State that the energy for diffusion comes from the kinetic energy of molecules and ions. 🧪

What is Diffusion?

Diffusion is the spontaneous movement of particles from an area of higher concentration to an area of lower concentration. Think of it like a crowded classroom where people (molecules) move to the empty seats (low‑concentration spaces) without any external push. 🌍

Energy Source for Diffusion

The driving force behind diffusion is the kinetic energy of the molecules and ions. Each particle moves randomly, and this motion is described by the equation:

$E_k = \frac{1}{2}mv^2$

Where:

• $m$ = mass of the particle
• $v$ = velocity of the particle

Because the particles are always moving, they collide and spread out, creating a net movement from high to low concentration. This is why diffusion does not need any external energy input. ⚡️

Examples & Analogies

• 💨 Air molecules: In a room, the smell of perfume spreads because the perfume molecules keep moving randomly.
• 💧 Water movement: In a plant root, water diffuses from the soil (high concentration) into the root cells (low concentration).
• 🧊 Ice melting: Heat energy increases the kinetic energy of water molecules, speeding up diffusion into the surrounding air.

Diffusion Rate Factors

Factor	Effect on Rate
Concentration Gradient	Higher gradient → Faster diffusion
Temperature	Higher temperature → More kinetic energy → Faster diffusion
Molecular Size	Smaller molecules diffuse faster
Medium (gas, liquid, solid)	Gases diffuse fastest, solids slowest

Exam Tips

• Remember: Energy source = kinetic energy of particles.
• Use the kinetic energy equation when asked to explain why diffusion occurs.
• Illustrate with a simple analogy (e.g., people moving to empty seats) to show understanding.
• When drawing a diagram, label the concentration gradient and indicate the direction of net movement.
• Check for keywords like “random motion”, “thermal energy”, and “concentration difference”.