These downloadable videos and animations are part of the multimedia package Stuff and Substance, developed by the Gatsby Science Enhancement Programme (SEP). They can be used to develop ideas relating to the intrinsic motion of particles and diffusion phenomena involving the liquid and gas states.

Due to the intrinsic translational movement of particles, samples of substances in the liquid and gas states will mix without the need for external agitation (stirring of some kind). Some students find it difficult to believe that the particles in a still volume of liquid are moving – they are happier to say the particles can be moved around. The gas state is less problematic. One animation is a formative assessment task which links particle diagrams to a diffusion experiment involving a coloured and colourless liquid. The video shows the classic diffusion experiment using ammonia and hydrogen chloride (evaporating from concentrated solutions). The second animation can be used to explain the difference between intrinsic motion of individual particles and bulk movement caused by external agitation.

These video and animation files form part of the resources in the section Diffusion in the Stuff and Substance multimedia package, which provides a series of interactive pages that can be used by teachers or students in the classroom.

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