   Chapter 20, Problem 108IP

Chapter
Section
Textbook Problem

# Although nitrogen trifluoride (NF3) is a thermally stable compound,  nitrogen triiodide (Nl3) is known to be a highly explosive material. NI3 can be synthesized according to the equation BN ( s ) + 3IF ( g ) → BF 3 ( g ) + NI 3 ( g ) a. What is the enthalpy of formation for NI3(s) given the enthalpy of reaction ( − 307 kJ) and the enthalpies of formation for BN(s) (−254 kJ/mol), IF(g) ( −96 kJ/mol), and BF3(g) ( − 1136 kJ/mol)?b. It is reported that when the synthesis of NI3 is conducted using 4 moles of IF for every l mole of BN. one of the by-products isolated is [IF2]+ [BF4]−. What are the molecular geometries of the species in this by-product? What are the hybridizations of the central atoms in each species in the by-product?

(a)

Interpretation Introduction

Interpretation: The reaction between BN and IF is given. The value of enthalpy of formation of NI3 is to be calculated from the given values. The molecular structure and hybridization of [IF2]+ and [BF4] is to be stated.

Concept introduction: The following steps are to be followed to determine the molecular structure of a given compound,

• The central atom is identified.
• Its valence electrons are determined.
• The value 1e is added to the total number of valence electrons for each monovalent atom present.
• The total number obtained is divided by 2 to find the number of electron pairs.
• This further gives the hybridization of the given compound.

To determine: The value of enthalpy of formation of NI3 .

Explanation

The value of enthalpy of formation of NI3 is 287kJ/mol_ .

Given

Enthalpy of reaction is 307kJ .

Enthalpy of formation for BN is 254kJ/mol .

Enthalpy of formation for IF is 96kJ/mol .

Enthalpy of formation for BF3 is 1136kJ/mol .

The reaction that takes place is,

BN(s)+3IF(g)BF3(g)+NI3(g)

The formula of ΔH° is,

ΔH°=npΔH°(product)nfΔH°(reactant)

Where,

• ΔH° standard enthalpy of reaction.
• np is number of moles of each product.
• nr is number of moles each reactant.
• ΔH°(product) is standard enthalpy of product at a pressure of 1atm .
• ΔH°(reactant) is standard enthalpy of reactant at a pressure of 1atm .

Substitute all values from the table in the above equation

(b)

Interpretation Introduction

Interpretation: The reaction between BN and IF is given. The value of enthalpy of formation of NI3 is to be calculated from the given values. The molecular structure and hybridization of [IF2]+ and [BF4] is to be stated.

Concept introduction: The following steps are to be followed to determine the molecular structure of a given compound,

• The central atom is identified.
• Its valence electrons are determined.
• The value 1e is added to the total number of valence electrons for each monovalent atom present.
• The total number obtained is divided by 2 to find the number of electron pairs.
• This further gives the hybridization of the given compound.

To determine: The molecular structure and hybridization of [IF2]+ and [BF4] .

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