I. CaCO3(s) CaO(s) + CO2(g)

Here are the chemical concepts represented by each equation, along with short notes:

i. $\text{CaCO}_{3(\text{s})} \xrightarrow{\Delta} \text{CaO}_{(\text{s})} + \text{CO}_{2(\text{g})}$
Concept: Thermal Decomposition
Note: This is a chemical reaction where a single compound breaks down into two or more simpler substances when subjected to heat.

ii. $2\text{NaOH}_{(\text{aq})} + \text{H}_2\text{SO}_{4(\text{aq})} \longrightarrow \text{Na}_2\text{SO}_{4(\text{aq})} + 2\text{H}_2\text{O}_{(\text{l})}$
Concept: Neutralization Reaction
Note: This is a reaction between an acid and a base, which produces a salt and water.

iii. $\text{CH}_{4(\text{g})} + \text{Cl}_{2(\text{g})} \longrightarrow \text{CH}_3\text{Cl}_{(\text{g})} + \text{HCl}_{(\text{g})}$
Concept: Substitution Reaction
Note: In this type of reaction, an atom or a group of atoms in a molecule is replaced by another atom or group of atoms.

iv. $\text{C}_6\text{H}_{12} \longrightarrow \text{C}_6\text{H}_{10} + \text{H}_2$
Concept: Elimination Reaction (specifically Dehydrogenation)
Note: This is a reaction where two atoms or groups are removed from a molecule, often resulting in the formation of a double or triple bond. In this specific case, hydrogen is removed.