Chapter 9, Problem 9.116SP

(a)

Interpretation Introduction

Interpretation:

Three resonance structures of $H_3^{+}$ ion have to be drawn.

Concept Introduction:

Resonance

Resonance is the phenomenon of delocalization of electrons of pi bond (either pi bonding or non-bonding or both) in a molecule such the molecule cannot be represented by a single Lewis structure as the delocalization of electrons gives rise to more than one structure to a same molecule.

Resonance structures

The various structures for a molecule that are formed by delocalization of electrons are termed as resonance structures.

Rules for writing resonance structures

All the resonance structures must have valid and appropriate Lewis structures.

The resonance structure are written and drawn such a way that position of atomic nuclei must not be changed.

Hybridization of atoms in the molecule must not be changed.

The position of bond (electrons) also known as distribution of electrons only must be changed.

All of the atoms involved in resonance and also the atoms that are directly bonded to those atoms must be coplanar (lie in same plane) nearly.

(b)

Interpretation Introduction

Interpretation:

From the given data enthalpy of the given reaction has to be calculated.

Concept Introduction:

$\Delta H°$ refers to change in enthalpy.  Change in enthalpy in a reaction and bond energy (BE) are related as,

    $\text{ΔH°}\text{=}\text{ΣBE(reactants)-ΣBE(products)}$

Hess’s law is applied to calculate the enthalpy changes in a reaction.  According to Hess’s law – “The overall enthalpy change of a reaction is equal to the sum of the enthalpy changes involving in each and every individual steps in the reaction.”  Thus if a reaction involves ‘n’ steps then enthalpy change $\Delta H°$ of the reaction is,

  $\Delta H°=\Delta {\text{H}}_1^{°}+\Delta {\text{H}}_2^{°}+\Delta {\text{H}}_3^{°}\mathrm{....}+\Delta {\text{H}}_n^{°}$