Question

Assertion A: The dihedral angles in H₂O₂ in gaseous phase is 90.2° and in solid phase is 111.5°.

Reason R: The change in dihedral angle in solid and gaseous phase is due to the difference in the intermolecular forces.
Choose the most appropriate answer from the options given below for A and R.7

विकल्प

• Both A and R are correct but R is not the correct explanation of A.

• A is correct but R is not correct.

• Both A and R are correct and R is the correct explanation of A.

• A is not correct but R is correct.

Answer 1

A is not correct but R is correct.

Explanation:

H₂O₂ and water combine in all amounts and have a structure that is somewhat comparable. Since hydrogen bonding in H₂O₂ affects the dihedral angle, H₂O₂ in the gas phase has a somewhat different structure from H₂O₂ in the solid phase.

The given images show structure of H₂O₂ in both gas and solid phase.

(a) Gas phase	(b) Solid phase

The structure of hydrogen peroxide is non- planar. The dihedral angle in gas phase 111.5° whereas, in solid phase the dihedral angle is 90.2°. H₂O₂ occurs in solid phase at 110 K.
The structure of H₂O₂ in gas phase is such that to minimize the repulsion between lone pairs and the O-H bond pairs. H₂O₂ structure is similar to that of an open book consisting 2 planes, such that each plane has one O-H bond pair.

H₂O₂ exhibits a skewed structure in both its solid and gaseous states due to the repulsion between its - OH bonds and the lone pairs of electrons on each of its O atoms. As a result, the molecule exhibits impeded rotation around a single bond. As hydrogen bonds weaken in the solid phase, the dihedral angle also decreases.

Hence, assertion A is incorrect but, reason R is correct.