Diffusion

Brownian Motion

Explanation and evidence for Brownian motion

• An example of Brownian motion is the observed jerky and erratic motion of smoke particles as they are hit by the unseen molecules in the air which can be seen under a microscope
• In 1905, physicist Albert Einstein explained that pollen grains in water were being moved by individual water molecules
• In all cases, larger and visible particles are caused to move by the random bombardment of smaller, invisible particles

Extended Only

Diffusion & Molecular Mass

• Diffusion occurs much faster in gases than in liquids as gaseous particles move much quicker than liquid particles
• At the same temperature, different gases do not diffuse at the same rate.
• This is due to the difference in their relative molecular masses
• Lighter gas particles can travel faster and hence further, therefore the lower its relative mass the faster a gas will diffuse

NH₃ molecules have less mass than the HCl molecule, so diffuse faster, hence the product (a white cloud of NH₄Cl) forms closer to the end where the HCl is