Types Of Reaction…

I posted this video a few years ago – it is rather crackly but it does explain things nicely. It describes several different kinds of reaction. The first sort it mentions is “synthesis” reactions – this is what we have been calling combination reactions. The only one that might be new is “double displacement” but if you think of it like a neutralisation reaction you should realise that it is in fact not that unfamiliar. Finally they also include “combustion” which perhaps I should include in our Types of Reaction pages too.

Each reaction animation is supported with a chemical symbol equation. Try to translate them into words; press pause then try to give names to the reactants and the products formed.

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One of the nice things about the animations is that it shows the individual atoms. You can see single atoms of an element, elements as a molecule (eg oxygen/O₂) and more complicated compounds containing two or more elements chemically joined together. Some of these reactions would have happened in a flash of heat, others would need heating to get them started and some would happen slowly in solution.

This is another video by the same crackly chap but with some actual reactions to watch this time.

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Combustion reactions are ones in which fuels combine with oxygen to produce one or more different oxides. The classic example is the hydrocarbon plus oxygen reaction producing carbon dioxide and water as the waste products. You may remember seeing the whoosh bottle demonstration (shown below) using an alcohol called propan-2-ol as the fuel.

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I don’t think that doing that in a glass bottle is very wise – if something did go wrong bits of flying glass are more harmful than pieces of polycarbonate plastic. I always use a hard plastic bottle when I do it; as does Steve Spangler below. He is using the alcohol ethanol as his fuel; it produces the same effect with less heat and less of a whoosh than propan-2-ol.

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He adds an excellent twist by sealing the lid of the bottle with his hand as the carbon dioxide and water vapour inside the bottle begin to cool. They contract, lowering the pressure inside the bottle, which is why the pressure of the atmosphere begins to crush the bottle. It is a little like the collapsing can video which you can see here.

Questions…

1. For the first video, what are the reactants for the following types of reaction…
   • (a) synthesis?
   • (b) decomposition (only one reactant)?
   • (c) single displacement?
   • (d) double displacement?
   • (e) combustion?
2. What are the reactants in the thermite reaction?
3. What would be the product of the sulphur and copper reaction shown in the second video?
4. What substance has the chemical formula C₂H₅OH?
5. What is the approximate air pressure at sea level in N/cm²?

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p.s. If you put too little fuel into the bottle, and don’t have oxygen as the limiting factor, you might end up with an explosive mixture. This would be unpleasant!