Page 36 - Curriculum Visions Dynamic Book

Spontaneous combustion
Spontaneous combustion is the effect of a material beginning
to oxidise very quickly. An oxidising agent, for example, readily reacts with another substance, giving up its oxygen. The reaction that transfers oxygen often causes the release of considerable amounts of heat (it is an exothermic reaction).
Demonstration of delayed oxidation
Potassium permanganate (an oxidising agent) and ethylene glycol (antifreeze) show the delayed effects of some chemical reactions. On their own these chemicals are harmless and will not catch fire. However, when mixed together they can be extremely dangerous.
When first mixed nothing appears to happen, because the chemicals need time to react. However, all the time the temperature is rising. Chemists call this waiting time an induction period. After a minute or two the chemicals suddenly reach a temperature where the reaction happens very fast indeed, and the mixture appears to burst into flame spontaneously.
 A few drops of ethylene glycol are added to crystals of potassium permanganate.
Hydrogen
Oxygen
Carbon
 A few minutes later the reaction speeds up and flames begin to shoot into the air.
EQUATION: Ethylene glycol and potassium permanganate
Ethylene glycol + oxidising agent ➪ carbon dioxide+ water C2H6O2(l) + 5O (from oxidising agent) ➪ 2CO2(g) + 3H2O(l)
 A molecule of ethylene glycol
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