The given chemical reaction shows the synthesis of ethylene from calcium carbonate $CaCO3$ through a series of steps. Here is the breakdown of each step:

CaCO3 is decomposed to form calcium carbide $CaC2$.Calcium carbide reacts with water to produce acetylene $C2H2$.Acetylene undergoes hydrolysis to form ethanol $CH3-CH2-OH$.Ethanol is chlorinated to form ethyl chloride $CH3-CH2-Cl$.Ethyl chloride then undergoes dehydrochlorination to yield ethylene $CH2=CH2$.

The overall chemical reaction can be summarized as follows:

CaCO3 -> CaC2 -> C2H2 -> CH3-CH2-OH -> CH3-CH2-Cl -> CH2=CH2

In this reaction pathway, each step involves different chemical transformations to eventually convert calcium carbonate into ethylene.