The three reactions in Cyberchemistry (diffusion is not a reaction) represent two of the four types of reactions that exist in chemistry. They are:
Single replacement reactions,
and Double replacement reactions.
A combination reaction can be represented like this, with A representing the first element or substance, and B representing the second element or substance, and with AB being the product.
As you can see, A combines with B to form AB.
A decomposition reaction is a reaction in which a substance, AB splits itself up into its components, A and B. This is shown below.
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Single Replacement Reactions
What happens in a single replacement reaction is this: A substance, C, exchanges itself for a component in a compound,AB, to form another compound, AC, and a single free molecule,B, as shown.
Double Replacement Reactions
A double replacement reaction is based on the same principle as the single replacement reaction, but, You start with two substances, AB and CD. Here A replaces C to form AD, but C joins with B, to form BC, as seen below.