Polyethylene is a polymer, meaning it's a large molecule made of repeating units. It's formed by the polymerization of the monomer ethylene. The chemical equation for this process is:

n CH2=CH2 → (-CH2-CH2-)n

where:

* n represents the number of repeating units in the polymer chain (and can vary significantly, resulting in different forms of polyethylene).

* CH2=CH2 is the chemical formula for ethylene, the monomer.

* (-CH2-CH2-)n represents the polyethylene molecule, where the repeating unit is -CH2-CH2-.

So, essentially, multiple molecules of ethylene (n) join together to form a long chain of repeating units, forming polyethylene.