Are decomposition and dissociation reactions the same?
Decomposition and disassociation refer to similar processes, however they are different. The main difference between them is that decomposition reactions are usually irreversible while disassociation reactions are reversible and exist in equilibrium. 

A decomposition reaction is where a compound breaks up into smaller elements or compounds. For example: $$\ce{2H2O -&gt; 2H2 + O2}$$ is an example of a decomposition reaction. Note that in this case that this is actually a reversible reaction.

A disassociation reaction is the general process where molecules split into smaller particles which can include elements, compounds, ions and radicals. For example: $$\ce{NaCl(s) -&gt; Na+ (aq) + Cl- (aq)}$$ is a disassociation reaction.