AP Chemistry
Worksheet : Obj 17-26-2
Name :
Date :
A. Review :
_____ 1. (T/F) NaF has a greater lattice energy than MgF2.
_____ 2. (T/F) MgO has a greater lattice energy than MgS.
_____ 3. (T/F) Lattice energy is endothermic.
_____ 4. (T/F) Carbon has a larger greater atomic radius than Nitrogen.
_____ 5. (T/F) Al3+ has a greater ionic radius than Mg2+.
_____ 6. (T/F) Sulfur has a greater electronegativity than O.
_____ 7. (T/F) The N-P bond is less polar than the N-O bond.
_____ 8. (T/F) Triple bonds are shorter than double bonds.
_____ 9. (T/F) Bond strengths are independent of their environment (i.e. a C-H bonds is always the same).
_____ 10. (T/F) Bond breaking is an exothermic process, making ΔH negative.
11. Use the following data to estimate ΔH°f for magnesium chloride.
Mg(s) + C12(g) ——> MgCl2(s)
Lattice Energy for MgCl2
-2957 kJ/mol
Ionization energy for Mg
735 kJ/mol
Ionization energy for Mg+
1445 kJ/mol
Electron affinity for Cl
-349kJ/mol
Bond energy of Cl2
239 kJ/mol
Enthalpy of sublimation for Mg
289 kJ/mol
A. Bond Energies
12. Use bond energy values (Table 8.4 – p. 351) to estimate ΔH for each of the following reactions in
the gas phase.
a. H2 + C12  2HC1
b. N≡N + 3 H2  2NH3
Ch. 8 and 9 : Ws – obj 17-26-2
13. Use bond energy values (Table 8.4) to estimate ΔH for each of the following reactions in the gas
phase.
14. Compare your answers from parts a and b of Exercise 12 with ΔH values calculated for each
reaction from standard enthalpies of formation in Appendix 4. Do enthalpy changes calculated
from bond energies give a reasonable estimate of the actual values?
15. The standard enthalpy of formation of NH3(g) is -46 kJ/mol. Use this and values for the N≡N and
H—H bond energies to estimate the N—H bond energy. Compare this result with the value in
Table 8.4.
B. Lewis Structures and Resonance
16. Write Lewis structures that obey the octet rule for each of the following. (First element is central
unless noted otherwise.)
a. H2CO(C is central)
c. CO2
b. SeF2
d. O2
17. Write Lewis structures for the following molecules or ions, which have central atoms that do not
obey the octet rule:
a. SF4
c. ClF5
b. XeF4
d. SF6
Ch. 8 and 9 : Ws – obj 17-26-2
18. Write Lewis structures for the following. Show all resonance structures where applicable.
a. NO3-
b. SCN- (Carbon is the central atom)
Formal Charge
19. Write Lewis structures that obey the octet rule for the following species. Assign the formal charge
for each central atom.
a.. XeO4
b. ClO3-
c. NO43-
Answers : 11. -947 kJ/mol 12a. -183 kJ 12b. -109 kJ
13. -92 kJ
14a. -184 kJ (close to the
-183 value) 14b. -92 (reasonably good) 15. N-H = 388.2 kJ/mol – good agreement with the
value of 391 kJ/mol from Table 8.4
17.
18.
19. Formal charges on central atom : a. Xe = +4 b. Cl = +2 c. N = +1
Ch. 8 and 9 : Ws – obj 17-26-2