Final answer:
The given reactions represent both thermal decomposition and thermal dissociation. Specifically, reactions b) and d) represent thermal decomposition where one substance breaks down into two or more different substances. Reaction c) is a thermal dissociation representing the decomposition of a compound into its elemental parts.
Step-by-step explanation:
Considering the given reactions, let's classify them as thermal decomposition or thermal dissociation. In general, thermal decomposition reactions involve a single compound breaking down into two or more components while thermal dissociation reactions encompass the breaking of compounds into elements. They're both heat-induced processes, differing mainly in the end products.
For the reaction a) N2 + 3H2 → 2NH3, it is a synthesis reaction rather than decomposition or dissociation. Reaction b) CaCO3 → CaO + CO2 and reaction d) NH4Cl → NH3 + HCl are both examples of thermal decomposition as a single compound is breaking down into two different products. In reaction c) 2HgO → 2Hg + O2, it's a thermal dissociation reaction where mercury(II) oxide (a compound) decomposes into elemental mercury and oxygen.
Learn more about thermal decomposition and thermal dissociation