Final answer:
Structural isomers C₂H₅OH and CH₃OCH₃ have the same gaseous densities at the same conditions but differ in vapor pressures, boiling points, melting points, and heats of vaporization due to different intermolecular forces.
Step-by-step explanation:
The structural isomers C₂H₅OH (ethanol) and CH₃OCH₃ (dimethylether) would be expected to have the same gaseous densities at the same temperature and pressure, assuming ideal behavior. This is because gaseous density for ideal gases depends only on the molecular weight and the temperature and pressure conditions, not on the molecular structure or the type of intermolecular forces present.
These two compounds would not be expected to have the same vapor pressures, boiling points, melting points, or heats of vaporization because these properties are influenced by the type and strength of intermolecular forces, which are different due to the different structural arrangements of the atoms within these molecules. Ethanol exhibits strong hydrogen bonding due to its hydroxyl (-OH) group, whereas dimethylether has weaker dipole-dipole and dispersion forces. As a result, ethanol has a higher boiling point compared to dimethylether.