Intermolecular forces are the attractions between molecules, which determine many of the physical properties of a substance. The intermolecular forces are generally a lot weaker than molecular bonding. For example, it requires 17 kJ/mol to overcome the intermolecular forces of liquid HCl to gaseous HCl. However, it requires much more energy, 431 kJ/mol , to break the covalent bonds between the hydrogen. and chlorine atoms.