8.9: Covalent Bond Properties

Bond Order

Exercise \(\PageIndex{1}\)

Linus Pauling noticed that the energy of a polar bond is often greater than expected. He attributed the greater bond energy to

1. a coulombic attraction between atoms with partially positive and negative charges.
2. the greater bond lengths of the heteronuclear bonds.
3. one of the many unexplainable phenomena that scientists encounter.
4. the ability of heteronuclear species to form double and triple bonds.
5. the greater number of valence electrons found in heteronuclear molecules.

Answer

a. a coulombic attraction between atoms with partially positive and negative charges.

Exercise \(\PageIndex{2}\)

In molecules, as bond order increases,

1. both bond length and bond energy increase.
2. both bond length and bond energy decrease.
3. bond length increases and bond energy is unchanged.
4. bond length is unchanged and bond energy increases.
5. bond length decreases and bond energy increases.

Answer

e. bond length decreases and bond energy increases.

Exercise \(\PageIndex{3}\)

Determine the bond order of NO⁺?

a. 2        b. 1.5        c. 1        d. 2.5        e. 3

Answer

e. 3

Exercise \(\PageIndex{4}\)

Use Lewis structures to predict the bond order for a sulfur-oxygen bond in SO₃^2-?

a. 1        b. 4/3        c. 5/2        d. 2        e. 3/2

Answer

a. 1

Exercise \(\PageIndex{5}\)

Use Lewis structures to predict the bond order for a sulfur-oxygen bond in the sulfite ion?

a. 1        b. 3/2        c. 4/3        d. 2        e. 5/2

Answer

c. 4/3

 

Bond Energy 

Exercise \(\PageIndex{6}\)

Based on the following data, what is the F-F bond energy?

 H₂(g) +  F₂(g) → HF(g); ΔrH = –272.5 kJ/mol-rxn

Bond     Bond Energy (kJ/mol)

H-H        435

H-F         565

a. 500 kJ/mol        b. 150 kJ/mol        c. –150 kJ/mol        d. –695 kJ/mol        e. 695 kJ/mol

Answer

b. 150 kJ/mol 

Cleavage of one H-H bond, \(\Delta H_{1}= 435 kJ/mol;\)

Cleavage of one H-F bond, \(\Delta H_{2}= 565 kJ/mol;\)

Formation of two F-F bonds, \(\Delta H_{3}= ?\)

ΔH_f of the reaction is = -272.5 kJ/mol = -545 kJ/2 mol

\(\Delta H_{f}=(\Delta H_{1}+\Delta H_{3})-(2*\Delta H_{2})\)

\(-545 = (435+\Delta H_{3})-(2*565)\)

\(-545 = (435+\Delta H_{3})-1130\)
\(585 = 435+\Delta H_{3}\)

\(153 kJ = \Delta H_{3}\)

Exercise \(\PageIndex{7}\)

Using bond-energy data, what is ΔrH for the following reaction?

CH₄(g) + 2Cl₂(g) → CCl₄(g) + 2H₂(g)

Bond     Bond Energy (kJ/mol)

C-H         413

H-H        432

Cl-Cl       242

C-Cl        328

a. –40 kJ/mol-rxn        b. –150 kJ/mol-rxn        c. 40 kJ/mol-rxn        d. 1415 kJ/mol-rxn        e. 150 kJ/mol-rxn

Answer

a. –40 kJ/mol-rxn 

Exercise \(\PageIndex{8}\)

Using the following data reactions:

                                                     ΔH° (kJ/mol-rxn)

H₂(g) + Cl₂(g) → 2HCl(g)                –184

H₂(g) → 2H(g)                                432

Cl₂(g) → 2Cl(g)                               239

calculate the energy of an H-Cl bond.

a. 92 kJ/mol        b. 855 kJ/mol        c. 487 kJ/mol        d. 428 kJ/mol        e. 244 kJ/mol

Answer

d. 428 kJ/mol

Exercise \(\PageIndex{9}\)

Which of the following species has the shortest carbon−nitrogen bond?

a. CH₃CN        b. CH₃N₂        c. CH₂NH        d. CH₃CONH₂        e. CH₃NH₃⁺

Answer

a. CH₃CN

Exercise \(\PageIndex{10}\)

Use the bond energies provided to complete the following statement.

 

________ when all of the bonds in acetic acid (CH3COOH) are broken.

 

Bond     Bond Energy (kJ/mol)

C-H         413

C-O        358

O-H        463

C=O       745

C-C         348

C=C        614

1. 3153 kJ/mol of energy is consumed
2. 3153 kJ/mol of energy is released
3. 2805 kJ/mol of energy is released
4. 2805 kJ/mol of energy is consumed
5. 2766 kJ/mol of energy is consumed

Answer

a. 3153 kJ/mol of energy is consumed