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TGQ1: Diffusion
Notes on the video of ammonia reacting with hydrogen chloride.
The reaction uses very concentrated solutions rather than pure samples in the gas state. Particles of the substances evaporate quickly from the solutions.
The particles of the two substances meet closer to the ‘hydrogen chloride end’ (left of image): this shows that the hydrogen chloride particles move more slowly than the ammonia particles. (The mass of each hydrogen chloride particle is greater than that of each ammonia particle, so on average the hydrogen chloride particles move more slowly).

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Language alert
Books often give the particles of a perfume spreading through a room as an example of diffusion. Individual movement of particles is involved, but it would take a very long time for them to spread throughout a room. Air currents will be speeding up the mixing.

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tgq1: notes

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