Two dichloroethylene molecules with the same chemical formula 1C2H2Cl22, but different arrangements of atoms are shown.
(c) Which form of dichloroethylene has the highest boiling point?

Isomerism refers to the phenomenon where two or more compounds have the same molecular formula but different structural arrangements of atoms. In the case of dichloroethylene, the two isomers, cis and trans, differ in the spatial orientation of the chlorine atoms around the double bond, leading to distinct physical and chemical properties.

The boiling point of a substance is the temperature at which its vapor pressure equals the external pressure, causing it to change from liquid to gas. Factors influencing boiling points include molecular weight, intermolecular forces, and molecular structure. Generally, isomers with stronger intermolecular forces, such as dipole-dipole interactions, will have higher boiling points.

Intermolecular forces are the forces of attraction or repulsion between neighboring particles (atoms, molecules, or ions). In dichloroethylene, the cis isomer has a higher dipole moment due to the arrangement of chlorine atoms, leading to stronger dipole-dipole interactions compared to the trans isomer, which can result in a higher boiling point for the cis form.