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TGG1: Particle Model explanation of evaporation
Students usually find it difficult to reconcile boiling – which happens at the boiling point - and evaporation – which happens at temperatures below the boiling point.

The video and images introduce the term evaporation and the start of a particle model explanation. Note that in these images we cannot show anywhere near the real number of particles in the dish. We are also not showing the particles of the dish itself.

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Students may need to be reminded that, when we considered boiling, we linked it to the idea that the particles have enough energy to escape from the hold of other particles. Clearly, particles must somehow be escaping from the hold of other particles for evaporation to occur, too. This raises the question of how the particles which escape get enough energy to do so when the temperature is so much lower than the boiling point: this is explained in the next topic, 'G2', which considers the relationship between the temperature of a sample and the energies of individual particles.

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Notes on the energy transfer animation
Some students may find it easier to see how an individual particle’s energy changes as a result of collisions if you ask students to choose a particle to follow before you start and then stop the animation again almost immediately. You may need to do this several times.

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tgg1: particle model
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