Covalent bond strengths are typically between 200 and 500 kJ mol-1. Hydrogen bonds are weak in comparison, they range from 5 to 40 kJ mol-1. Van der waals forces are weaker still having a strength of about 2 kJ mol-1. Hydrogen bonds and Van der waals forces are not strong enough to influence the chemical behavior of most substances, although they may affect the physical properties of substances. The heat of solvation arises when an ionic substance is dissolved in a polar solvent.
Intermolecular bonds form between polar solvent and ionic substance molecules.
Bonds that are within the ionic lattice between molecules are broken as charged molecules are attracted to solvent molecules. Ionic lattice bonds that are broken release more energy than the energy put into the newly formed intermolecular bonds this explains why an exothermic reaction occurs. The tetrachloromethane which has a symmetrical tetrahedral shape is a non-polar substance so no intermolecular attractions between molecules occur. Since there are no intermolecular attractions, no forces are created which can attract NaCl molecules away from their ionic lattice. In the case of NaCl and ethanol the polar molecules forms intermolecular attractions with charged NaCl molecules, pulling the molecules away from the ionic lattice and therefore allowing NaCl to dissolve in ethanol.