The standard heat of vaporization, AHo vap of He is 0.1 kJ/mol and that of Br, is 15.0 kJ/mol.
a. Identify the type(s) of intermolecular force(s) that exists in pures samples of each compound.
Helium (He) is a noble gas and exists as individual, non-polar atoms in its pure state. The intermolecular forces present in pure helium are weak London dispersion forces.
Bromine (Br2) is a diatomic molecule with polar covalent bonds. The intermolecular forces present in pure bromine are dipole-dipole interactions and London dispersion forces.
b. Explain the significance of the difference in the standard heat of vaporization between helium and bromine.
The difference in the standard heat of vaporization between helium and bromine can be attributed to the difference in the strength of the intermolecular forces present in each compound. Helium, being a noble gas with weak London dispersion forces, requires less energy to break the intermolecular forces holding the atoms together, resulting in a lower heat of vaporization. In contrast, bromine, with stronger dipole-dipole interactions and London dispersion forces, requires more energy to break these forces and transition from a liquid to a gaseous state, resulting in a higher heat of vaporization.