Types of Reactions

There are probably millions of reactions.

We can’t remember them all, but luckily they will fall into several categories.

the 5 major types.

1. Combination Reactions

2. Decomposition Reactions

3. Displacement Reactions

4. Double displacement Reactions

5. Oxidiation and Reduction Reactions

Combine = put together2 substances combine to make one compound (also called “synthesis”)Ca + O2 → CaOSO3 + H2O → H2SO4

We can predict the products, especially if the reactants are two elements.

Those reactions in which two or more substance combine to form a single substance, are called COMBINATION REACTIONS.

Separation of a substance into two or more substances that may differ from each other and from the original substance called DECOMPOSITION REACTION.

decompose = fall apart

one reactant breaks apart into two or more elements or compounds.

NaCl → Na + Cl2

CaCO3 → CaO + CO2

Note that energy (heat, sunlight, electricity, etc.) is usually required

One element replaces anotherReactants must be an element and a compound.Products will be a different element and a different compound.Na + KCl → K + NaCl F2 + LiCl → LiF + Cl2

DISPLACEMENT REACTION a reaction in which an elementary substance displaces and sets free a constituent element from a compound.

EXAMPLE

In DOUBLE DISPLACEMENT reactions two ionic compounds switch cations.

Two things replace each other.Reactants must be two ionic compounds, in aqueous solution

Example Na2CO3(aq) + 2HCl(aq) → 2NaCl(aq) + H2CO3(aq)

Oxidiation:1. The addition of oxygen to a substance is called oxidation2. The removal of Hydrogen from a substance is also called oxidation.

Reduction:1. The addition of Hydrogen to a substance is called Reduction.2. The removal of oxygen from a substance is also called Reduction.

For example, in the burning of hydrogen2H2 + Ο2 −> 2H2O

The combination of nitrogen and oxygen which occurs at high temperatures\ follows the same pattern.

N2 + O2 −> 2NO

Gain and Loss of Hydrogen

The original view of oxidation and reduction is that of adding or removing oxygen . An alternative approach is to describe oxidation as the loss of hydrogen and reduction as the gaining of hydrogen. This has an advantage in describing the burning of methane.

CH4 + 2O2€−> CO2 + 2H2O

With this approach it is clear that the carbon is oxidized (loses all four hydrogens) and that part of the oxygen is reduced (gains hydrogen). Another reaction where the hydrogen approach makes things clearer is the passing of methanol over a hot copper gauze to form formaldehyde and hydrogen gas (Hill and Kolb):

CH3OH -> CH2O + H2