Name:_____________________________
CHEM 1311A
Second Exam
22 February 2002
In taking this examination, you are expected to adhere to the GT academic honor code. At a minimum this requires that
you utilize only the materials supplied to you (except for a non-programmable calculator), and that you do not give help
to, or accept help from, others.
1. (15 points) Draw a thermochemical cycle (Born-Haber cycle) for the formation of CaO from solid calcium
metal and oxygen gas based on the given enthalpy values. Label each step with the appropriate thermodynamic
quantity, and calculate the enthalpy of formation for CaO(s).
CaO lattice energy
Ca atomization energy
Ca first ionization energy
Ca second ionization energy
O2 bond energy
O first electron affinity
O second electron affinity
3401 kJmol–1
178 kJmol–1
590 kJmol–1
1145 kJmol–1
494 kJmol–1
–140 kJmol–1
+744 kJmol–1
2. Silver oxide (Ag2O) crystallizes in the Cuprite structure.
a) (4 points) How many silver and oxygen atoms contains the unit cell of Ag2O shown below?
b) (8 points) Calculate the density of silver oxide in gcm–3 (the unit cell dimension is 4.723Å, the larger
spheres represent silver cations, the smaller spheres the oxide anions, Avogadro's Number
NA=6.022x1023).
3. (8 points) The standard enthalpy of formation DHf(298K) becomes less negative along the series LiF, NaF,
KF, RbF, CsF, but more negative along the series LiI, NaI, KI, RbI, CsI. Explain briefly.
4. (70 points) Circle the letter corresponding to the correct answer for each of the following:
A representation for one of the molecular orbitals of carbon dioxide is shown below:
y
z
x
What atomic orbital of carbon contributes to this molecular orbital?
a) 2s
b) 2px
c) 2py
d) 2pz
What is the character of the depicted molecular orbital?
a) non-bonding
b) sigma bonding
c) sigma anti-bonding
d) pi bonding
e) pi anti-bonding
Which of the following salts will have most likely the highest melting point?
a) MgF2
b) NaCl
c) MgCl2
d) ZnF2
Which of the following ions will have most likely the greatest heat (enthalpy) of hydration?
a) Li+
b) Fe3+
c) Zn2+
d) Ru3+
Which of the following salts will have most likely the greatest lattice energy?
a) NaCl
b) MgF2
c) MgCl2
d) LiF
Which of the following salts would be expected to have the greatest solubility in water?
a) NaCl
b) MgCl2
c) KI
d) CaBr2
Based upon consideration of size ratios, in which of the following salts are the cations most likely eight
coordinate?
a) NaCl
b) CsCl
c) LiCl
d) KCl
When ammonium chloride (NH4Cl) is dissolved in water, heat is absorbed from the surroundings. Which of the
following statements is incorrect with respect to this observation:
a) The free energy change is negative
b) The entropy change is negative c) The enthalpy change is positive
Which of the following four band structure diagrams corresponds to a p-type semiconductor?
energy
a)
b)
c)
d)
What dopand would you add to silicon in order to get a n-type semiconductor?
a) As
b) Ga
c) B
d) none, Si is already a n-type semiconductor
What is the hybridization of the oxygen atoms in carbon dioxide?
a) sp
b) sp2
c) sp3
d) not hybridized
Which of the following molecules does not have a dipole moment?
a) CHCl3
b) H2O
c) BCl3
e) none (all four molecules have a dipole moment)
e) PH3
Which of the following species do you expect to have the highest boiling point?
a) SiCl4
b) SnCl4
c) CCl4
d) GeCl4
Which of the following species do you expect to have the greatest bond energy?
a) HCl
b) HBr
c) HI
d) HF