Diffusion | Chemistry for Grade 11 (IGCSE) PDF Download

Diffusion

• This is the process by which different gases or different liquids mix and is due to the random motion of their particles.
• Diffusing particles move from an area of high concentration to an area of low concentration.
• Eventually the concentration of particles becomes even as they spread out to occupy all of the available space.
• Diffusion occurs spontaneously and does not require energy input, although it happens faster at higher temperatures.

Diffusion & Molecular Mass

• Diffusion happens more rapidly in gases compared to liquids because gas particles move at a higher speed than liquid particles. 
• However, at the same temperature, different gases don't diffuse uniformly due to variations in their relative molecular masses. 
• Lighter gas particles have the ability to travel faster and cover more distance, resulting in faster diffusion for gases with lower relative masses. 
• This phenomenon can be observed in a reaction involving ammonia (NH₃) and hydrogen chloride gas (HCl) in a lengthy glass tube. 
• The formation of white smoke, representing ammonium chloride (NH₄Cl), occurs closer to the end of the tube, contrary to the expected middle section, because hydrogen chloride (with a molecular mass of 36.5) and ammonia (with a molecular mass of 17) have smaller and lighter molecules.