12 .Assertion : SiCl4 reacts with water,CCl4 does not. Reason :SiCl4 is ionic whereas CCl4 is covalent. 13. Assertion : Energy of resonance hybrid is equal to the average of energies of all canonical forms. Reason : Reason hybrid cannot be presented by a single structure.
12. Assertion and Reasons are both true and it is the correct explanation.
Si has d-orbitals to accept electrons donated by water but C does not.
Therefore,
SiCl4SiCl4
reacts with water but
CCl4CCl4
does not.
13. Assertion is not correct but Reason is correct
Resonance hybrids are always more stable than any of the canonical structures would be, it they existed. The delocalisation of the electrons lowers the orbital energies, imparting stability. The gain in stability of the resonance hybrid over the most stable of the canonical structure is called resonance energy.
A canonical structure that is lower in energy makes a relating greater contribution to resonance hybrid. Thus, the correct assertion will be energy of resonance hybrid is equal to the sum of energies of all canonical forms in proportion of their contribution towards the resonance hybrid.
