Why are decomposition reactions called the opposite of combination reactions? Write equations for these reactions.
Decomposition reactions are those in which a compound breaks down to form two or more substances. These reactions require a source of energy to proceed. Thus, they are the exact opposite of combination reactions in which two or more substances combine to give a new substance with the release of energy.For Example:
CaCO3 (s) `""/Delta`>CaO(s)+CO2 (g)
CaO (s) + H2O (l) → Ca(OH)2 (aq)
In decomposition reaction, a compound breaks down to two or more simple products, whereas in combination reaction, two or more reactants combine to form a single product. Therefore, both the reactions are opposite to each other.
For example, in a combination reaction, simple molecules of hydrogen and oxygen combine to form a water molecule.
2H2 (g) + O2 (g) → 2H2O (l)
While in decomposition reaction, reverse process takes place—i.e., water decomposes to hydrogen and oxygen.
2H2O (l) → 2H2 (g) + O2 (g)