Name: _______________
(2 points !)
Final Exam
Chem 112
Fall 2006
All questions worth 18 points
Recent Material - Questions 1-9. You may skip 1 question this section.
1. In this chapter you learned bout 2 different type of calorimeters, a constant volume
calorimeter and a constant pressure calorimeter. How were these different? Which
one measured )H, which one measures )E, and why?
Constant Volume - ‘Bomb’ calorimeter- reaction takes place inside a sealed steel
sphere so volume cannot change. Since qv = )E, measures )E.
Constant Pressure - ‘coffee-cup’ calorimeter - reaction takes place inside an insulated
cup, you assume that the pressure doesn’t change over the time that you do the
experiment. Since qp=)H, measures )H
2. I have a reaction that lowers the temperature of 50 g of water from 25.0oC to 23.0oC.
If I do this same reaction in a calorimeter with 50 g of acetone and the initial
temperature is also 25.0o C, what is the final temperature?
(The heat capacity of water is 4.18 J/ oC@g, the heat capacity of acetone is 2.17 J/ oC@g)
Heat of reaction measured in water = s.h.c. x g x )T
=4.18 x 50 x -2 = -418 j
Will have the same heat of reaction in acetone so:
-418 = 2.17 x 50 x (Tf-25)
-418/(2.17x50) = Tf-25
-3.85 = Tf-25
25-3.85 = Tf = 21.15oC
3. Use the following table of )H0f values to calculate )H for the reaction 2Na(s) +
2H2O(l)6 2NaOH(aq) + H2(g)
Compound
)H0f (kJ/mol)
Na(s)
0(0)
Na+(aq)
-240
H2O(l)
-286
H2O(g)
-242
NaOH(s)
-427
NaOH(aq)
-470
H2(g)
0
H(g)
217
2
4. Light was a wavelength of 350 nm is considered to be in the UV-A range. What is
the energy of a single photon of light of this wavelength? What is the energy of a mole
of photons at this wavelength?
E=h( =hc/8 = (6.626x10-34 x 2.998x108)/350x10-9
= 5.676x10-19 J
1 mole of photons
E = 5.676x10-19 J x 6.022x1023
=341.8 kJ
5. In class we discussed 4 quantum numbers that are used in describing the orbitals of
electrons. What are these 4 numbers, What symbols to we give them, what range of
values can they have, and what is their physical meaning?
Principal Quantum Number (n), n=integers >0, gives the overall energy or size of an
orbital
Angular Momentum Number (R) R = 0....n-1, give the shape of the orbital (0=s=
spherical, 1 = p = 2 lobes, 2=d = 4 lobes, 3=f=8 lobes)
Magnetic Quantum Number (mR) mR=-R...+R, gives orientation of orbital
Electron Spin Quantum Number (ms) ms = +1/2 or -1/2 , gives the spin of the electron in
the orbital
6. Rank the following atoms or ions in the by their properties
B, In, Rb
Smallest atom __B__,_In__, _Rb__ Largest atom
B, Ba, Be
Lowest ionization energy _Ba__, _Be__, __B__ Largest ionization energy
Ga, Se, O
Most negative electron affinity __O__, _Se__, _Ga__ Least negative electron affinity
As, Br, F
Smallest electronegativity _As__, _Br__, __F__ Largest electronegativity
Ar, I-, K+, Mg2+, O2-, P3-, Se2-,Sr2+
Smallest _Mg2+, _O2-_, _K+__, _Ar__, _P3-_, _Sr2+, __Se2-, _I-__ Largest
3
7. In the following pairs of ionic compounds, circle the compound with the LARGEST
lattice energy
A. NaCl or KCl
B.
LiF or CsF
C. Mg(OH)2 or MgO
D.
Na2SO4 or CaSO4
E. MgO or BaS
F.
NaBr or KI
8. Estimate )Hrxn for the following reaction using the table of bond energies given
below:
CO (g) + 2H2(g) 6 CH3OH(g)
Bond
Energy
(kJ/mol)
C-H
413
C-O
358
C=O
745
C/O
1072
O-H
467
H-H
432
H=H
895
4
9. Give the
A. Lewis Structure
B. Electron geometry
C. Molecular geometry, and
D. bond angles
for each of the following molecules also tell if the molecule is
E. Polar or Non-polar
CF4
SO2
Tetrahedral
Tetrahedral
109
Non-polar
SeF4
Trigonal Planar
V shaped
120
Polar
KrF4
Trigonal bipyramid
See-saw
120 & 90
polar
NO3-
Octahedral
Square planar
90
Non-polar
KrO4
Tetrahedral
Trigonal pyramid
<109
polar
Tetrahedral
Tetrahedral
109
Non-polar