HW 2. CHEM 481 Chapters 3 & 5
Chapter 3.
Name:________________________
Energetics of Ionic Bonding
1. Give coordination number for both anion and cation of the following ionic lattices.
a) CsCl Structure:
b) Rock Salt Structure:
c) Fluorite Structure:
d) Sphalrite Structure:
e) Wurtzite:
f) Rutile:
2. Calculate the number of formula units in the unit cell of the following metallic and
ionic compounds.
a) NaCl(fcc)
b) CsCl(bcc)
c) ZnS(fcc)
d) CaF2(bcc)
3. What is Coulombs law how it applies to ionic bond?
4. What is lattice energy? Take NaCl as an example.
5. Place the following compounds in order of increasing lattice energy: a) magnesium
oxide b) lithium fluoride c) sodium chloride. Give the reasoning for this order.
6. Explain the lattice energy and melting point trends:
Compound
Cation radius Anion radius Melting Point Lattice Energy
(Angstroms) (Angstroms) (Centigrade)
(kcal/mol)
MgCl2
0.65
1.81
714
2326
CaCl2
0.94
1.81
782
2223
MgO
0.65
1.45
2852
3938
CaO
0.94
1.45
2614
3414
7. Why is Madalung constant for NaCl is significantly different from CaF2 value and
why is it different for different ionic lattice types?
Ionic Solid Madelung Constant
NaCl
CaF2
1.747558
2.51939
Coor. #
Lattice Type
A:C
6 : 6 Rock salt
8 : 4 Fluorite
8. Calculate the first two terms of the series for the Madelung constant for the cesium
chloride lattice. How does this compare with the limiting value?
9. In calculating lattice energy, why should Coulombs law equation is multiplied by the
Avogadro’s number, N and Madelung constant, A?
N z2e2
Lattice Energy = - ------ x
4or
N
N A z2e2
x A = - -------4or
10. In the correction to lattice energy what is factor n in Born-Lande equation accounted
for and how it relate to electronic configuration?
11. Using the Born-Lande equation, calculate the lattice energy of cesium chloride.
Lattice Energy
N A z2e2
1
= - ------ ( 1 - ---)
4or
n
12. What are Born-Mayer and Kapustinskii equations? How are they different from the
Born-Lande equation?
13. What is a Born-Haber cycle?
14. Calculate the Lattice energy of NaCl from following thermodynamic data:
1.
2.
3.
4.
Steps
Vaporization of sodium: Na(s)
 Na(g)
Decomposition of Cl2: 1/2 Cl2 (g)  Cl(g)
Ionization of sodium: Na(g)  Na+(g)
Electron affinity to chlorine: Cl(g) + e-  Cl-(g)
Ho, kJ
+92
+121
+496
-349
5. Formation of NaCl(s):
Na(g)+1/2Cl2 (g)
 NaCl(s) -411
15. Construct a Born-Haber cycle for the formation of aluminum fluoride. Do not
perform any calculation.
16. Define following terms:
a) Enthalpy of solution, Hsolution:
b) Enthalpy of hydration, Hhydration:
c) Solvent-solvent intermolecular attractions, Hsolvent-solvent:
17. How is Enthalpy of solution, Hsolution, Enthalpy of hydration, and Lattice energy are
related?
18. Predict the solubility of following ionic compounds:
Lattice Energy(U)
Hhyd, M+
LiF
1030
-950
LiI
720
-950
CsI
585
-700
MgF2 3100
-2800
a) LiF:
b) LiI:
Hhyd, M-60
-80
-80
-120
c) CsI:
d) MgF2:
19. Give rational explanation to the solubility rules in terms of ioin sizes, lattice
energy(U), Hhyd, and Hsolution.
a) All compounds containing alkali metal cations and the ammonium ion are soluble.
b) All compounds containing NO3-, ClO4-, ClO3-, and C2H3O2- anions are soluble.
20. Calculate the enthalpy of formation of calcium oxide using a Born-Haber cycle.
Obtain all necessary information from the data tables in the Appendices. Compare
the value that you obtain with the actual entropy measured value of Hf(CaO(s)).
21. Although the hydration energy of the calcium ion, Ca2+, is much greater than that of
the potassium ion, K+, the molar solubility of calcium chloride is much less than that
of potassium chloride. Suggest an explanation.
HW 2. CHEM 481 Chapters 3 & 5
Chapter 5 Redox Chemistry
Name:________________________
1. Which of the following reactions is redox?
a) NaCl + AgNO3  AgCl + NaNO3
b) NaOH + HCl
 NaCl + H2O
c) Zn + 2HCl
 ZnCl2 + H2
d) 2Cr + 6HCl
 2CrCl3 + 3H2
e) MnO2 + 4HBr Br2 + MnBr2 + 2H2O
2. Separate the reduction and oxidation half reactions in following chemical equations.
a) Zn + 2HCl  ZnCl2 + H2
b) MnO2 + 4HBr  Br2 + MnBr2 + 2H2O
c) 10K + 2KNO3  N2 + 6K2O
3. Balance following reactions that take place and give the sum of stoichiometric
coefficients.
a) Cr2O72-(aq) + Cl-(aq) ----- Cr3+(aq) + Cl2(g) (acid solution)
b) Br-(aq) + MnO4(aq)
----- Br2(g) + Mn2+(aq) (acid solution)
c) Al(s) + MnO4-(aq)
----- MnO2(s) + Al(OH)4-(aq) (basic solution)
4. Construct a Galvanic cell employing following reactions:
a) Ni(s) + Cu2+(aq)  Ni2+(aq) + Cu(s)
b) Zn(s) + 2H+(aq)  Zn2+(aq) + H2(g)
5. Using the E0 values given in the table calculate the Eocell for reactions in problem 4 and
identify following:
a) two half reactions; b) anode; c) cathode; d) direction of electron flow through the
external wire.
6. Calculate the G0 value for reactions in problem 4.
7. Using Ellingham diagram find out the minimum temperature required for the reduction
of SiO2 by C. Please write the redox reactions involved.
8. Estimate the potential difference required to reduce TiO2 to metal at 10000C.
9. Using Lattimer diagram(Appendix 2) calculate the E0 for the reduction of HClO3 to
HClO in aqueous acidic solution.
10. Write balanced half-reactions for the reduction of NO to N2O and N2O to N2 in basic
solution.
Is N2O thermodynamically stable with respect to disproportionation to NO and N2 in
basic solution? What is Go?