Page 24 - Curriculum Visions Dynamic Book

Demonstrating nitrogen-based explosives
Solids and liquids occupy very little volume compared with the same number of molecules of a compound as a gas. The rapid change from solid or liquid to gas is the key to creating an explosion.
An explosive is a substance that is normally unreactive, but which can be made to react very violently, changing from a solid or a liquid to a gas. The explosion is created because of the pressure of the expanding gas on surrounding solid or liquid materials.
Many explosive materials simply burn when
they are not contained in some form of packing. Thus, for example, gunpowder can be laid as a trail of powder to make a burning fuse, but if the trail leads to gunpowder confined in a barrel, the gunpowder will explode. This shows that the process of burning is quite slow, and that a container is needed so that pressure can build up to give an explosive effect.
Many materials can be made explosive. For example, petrol vapours can explode, as can coal dust and even flour dust. Thus, providing a material with
a large amount of surface area – as happens with powders – also helps to create an explosion.
 Orange ammonium dichromate crystals are dense and occupy relatively little space. During the reaction shown, nitrogen is released as a gas, leaving green chromium oxide behind.
 The relative space occupied
by a solid, liquid and a gas helps
us to understand the effect of explosives. A sudden change of state of a substance from a solid to a gas creates a rapid expansion and consequent displacement of whatever material is around that substance.
Solid
Liquid
Gas
Chromium oxide
Ammonium dichromate
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