What is the sign of ∆H when breaking intermolecular bonds between solute molecules?

When breaking intermolecular bonds between solute molecules, the sign of ∆H is positive. This is because breaking bonds requires energy input. In the context of thermodynamics, when a process absorbs heat or energy from the surroundings, it is endothermic, resulting in a positive change in enthalpy (∆H).

In the case of breaking intermolecular forces, such as hydrogen bonds, dipole-dipole interactions, or van der Waals forces, energy must be supplied to overcome these attractions between the solute molecules. Therefore, since energy is being absorbed to facilitate the separation of these molecules, the enthalpy change associated with this process will be positive.

This aligns with the fundamental principle of bond energies: energy is required to break bonds, whether they are intramolecular (between atoms within a molecule) or intermolecular (between molecules). Understanding this concept is crucial in thermochemistry, as it helps explain solvation processes, phase changes, and reaction dynamics in various chemical contexts.