There are five general types of chemical reactions. synthesis decomposition single replacement double replacement and oxidation
A chemical reactions is one where the composition of the molecules and the chemical bonding between atoms is changed.
In a synthesis two atoms or molecules are joined together to make one molecule .
The single bonds between the hydrogen atoms is broken and new single bonds are formed to the oxygen atom. The double bond between the oxygen atoms is broken and new bonds are formed with the hydrogen.
In a decomposition reaction the bonds inside of a molecule are broken allowing it to break apart and become more than one molecule.
In carbonic acid the bonds between one of the oxygens and carbon are broken allowing the oxygen to bond with both of the hydrogens that are in a resonance structure in the molecule. This leaves the carbon as carbon dioxide and water.
In a single replacement reaction one element that is more reactive takes the place of a less reactive element.
Example Zn +2 HCl ========
The bond between the hydrogen and the Chlorine is broken as the Chlorine is more attracted to the Zinc with a lower electro negativity than the Hydrogen. new bonds are formed between the Zinc and two atoms. Also the two Hydrogen atoms bond together to make Hydrogen gas.
In a double replacement reaction two molecules change. The positive atoms of the molecules join to different negative atoms.
Sometimes this results in an oxidation reduction reaction where the charges on the atoms also change.
( Note an oxidation redaction reaction can be consider a another form of a chemical reaction.)
The bonds between the Na and Cl break as do the bonds between the Ag and the nitrate ion
Oxidation reactions can be considered to be special types of synthesis and decomposition. Oxidation is a common chemical reaction involving Oxygen