Animations and Videos: More about Substances

These downloadable videos and animations are part of the multimedia package Stuff and Substance, and are intended to be used to establish the concept of a substance. The individual video and animation files are provided separately here to allow flexibility in their use. The Stuff and Substance multimedia package provides a series of interactive pages that can be used by teachers or students in the classroom, including supporting commentary and questions, animations, videos, images, and teachers’ notes. This section builds on ideas introduced earlier on in Stuff and Substance.

Further developments of understanding are:

• Pure samples of substances in the solid state usually consist of crystals, even though this is sometimes not obvious.
• Melting and boiling require an energy input for the change of state to take place. Thus the temperature remains at the melting point while a substance changes from the solid to liquid state. Water requires a lot of energy to change from liquid to gas. Therefore, efficient cooling by means of a Liebig condenser is needed to condense gaseous water (i.e. remove a lot of energy).
• The gas state exerts a pressure which depends on the concentration and energies of the particles. Boiling points depend on the external pressure.