There will be a decrease as noted in the problems in the text because the VDF equation takes into effect the intermolecular forces. See Figure 13.37 and Figure 13.39 in your text. Now it is ready to inter molecularly bond to another highly electronegative atom in another molecule. This resultant bond between the H atom in one molecule and a highly elecronegative atom in another molecule is an intermolecular hydrogen bond. O can all have hydrogen bonds between different molecules.
Methanol is polar and can have dipole-dipole bonds.
So between the two we can only have dipole-induced dipole forces. Again, we need to show how an OH- group forms 5. An example is HCl. Lewis acid HS- is Lewis base 11.