Solid vs liquid benzoic acid

[Yngevege]

Basically I want to know which bondings are broken when going from the solid phase to the liquid phase.

I know that benzoic acid makes dimers (though only in gas phase, some say?) and that they have Van der Waals' forces between their rings. I tried to use my knowledge about water: Water have 4 hydrogen bonds in solid phase but less in liquid (avg 3,4?), does the same apply to benzoic acid?

Does anyone have any qualified guesses?:shy:

Basically I want to know which bondings are broken when going from the solid phase to the liquid phase.

 

[chemisttree]

The dimer is through the carboxylic groups. It is seen in the NMR if the right solvent is chosen.

 

[quicknote]

The transition from solid to liquid phase in benzoic acid involves breaking intermolecular bonds, specifically Van der Waals forces, which are weaker than the intramolecular bonds holding the molecule together. In the solid phase, benzoic acid molecules are arranged in a crystal lattice structure, held together by Van der Waals forces between the aromatic rings of adjacent molecules. These forces are relatively strong, as evidenced by the high melting point of benzoic acid (122.4°C).

As the temperature increases and the solid benzoic acid is heated, the molecules gain enough energy to overcome the intermolecular forces and break apart from the crystal lattice. This results in a transition to the liquid phase, where the molecules are free to move and rotate without the constraints of the crystal lattice. In the liquid phase, the Van der Waals forces between molecules are weakened, resulting in a lower boiling point (249.2°C) compared to the melting point.

It is important to note that although benzoic acid can form dimers in the gas phase, these dimers are not present in the solid or liquid phases. In the solid phase, the dimers are broken apart due to the strong intermolecular forces between adjacent molecules. In the liquid phase, the molecules are no longer close enough to form dimers.

In summary, the transition from solid to liquid phase in benzoic acid involves breaking intermolecular bonds, specifically Van der Waals forces, which results in a decrease in the number and strength of these bonds compared to the solid phase.