Which substance in each of the following pairs would you expect to have larger dispersion forces? (b) HCl or HI

Dispersion forces, also known as London dispersion forces, are weak intermolecular forces that arise from temporary fluctuations in electron density within molecules. These fluctuations create instantaneous dipoles, which induce dipoles in neighboring molecules, leading to an attractive force. Dispersion forces are present in all molecules, but they are particularly significant in larger, more polarizable molecules.

Polarizability refers to the ability of an electron cloud around a molecule to be distorted by an external electric field or nearby charges. Larger molecules with more electrons have greater polarizability, resulting in stronger dispersion forces. In comparing substances, the one with the larger atomic or molecular size typically exhibits stronger dispersion forces due to its increased polarizability.

When comparing HCl (hydrochloric acid) and HI (hydroiodic acid), it is essential to consider their molecular weights and sizes. HI is larger and has more electrons than HCl, leading to greater polarizability and, consequently, stronger dispersion forces. Therefore, in this pair, HI would be expected to have larger dispersion forces due to its size and electron cloud characteristics.