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A demonstration of a rapid change of state using liquid nitrogen. A melted ice lolly is submerged in liquid nitrogen, at which point it turns back into an ice lolly and is frozen. This demonstrates a rapid change of state. The experiment is repeated using a balloon full of air. A cartoon is used to illustrate particle theory of a gas turning to a liquid and vice versa.
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First broadcast:
11 October 2007

Classroom Ideas

This clip can be used as part of a topic on 'gases around us' to explain what happens to particles in a liquid and a gas once cooled and heated. By pausing the clip before the balloon is plunged into the liquid nitrogen, pupils could be asked to predict what will happen to air in the balloon once cooled, thus assessing their understanding of condensation. In addition, they could predict what will happen to the liquid as it is re heated. Are they able to predict that the balloon will expand due to the behaviour of particles in a gas? After the cartoon explanation of particle theory has been shown, pupils could re-enact the changes that occur on heating and cooling different substances. By taking on the role of a particle, each pupil works in a group to show the effect on the arrangement of particles when they are heated or cooled eg in your group, show how the particles are arranged in a block of ice (pupils could pack themselves together tightly with linked arms). As the ice is heated, show how the particles are now arranged. What happens if the water is heated further?

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