Physical change or Chemical change

Physical change is change of temperature, appearance, ... but no change in chemical content.
Chemical change is a change of chemical content.
So, cracking and fractional distillation are physical change. Polymerisation is chemical change.

cracking and polymerisation are chemical change ( bonding form or break )

cracking is the process whereby complex organic molecules such as kerogens or heavy hydrocarbons are broken down into simpler molecules (e.g. light hydrocarbons) by the breaking of carbon-carbon bonds in the precursors.

polymerization is a process of bonding monomers, or "single units" together through a variety of reaction mechanisms to form longer chains named polymers


fractional distillation is physical change ( no bonding form or break )

Fractional distillation is the separation of a mixture into its component parts, or fractions, such as in separating chemical compounds by their boiling point by heating them to a temperature at which several fractions of the compound will evaporate.

i thk cracking and polymerization is chemical change while fractional distillation is physical