Download Chemistry 105A Exam II - November 6, 2009 and more Exams Chemistry in PDF only on Docsity!
Chemistry 105A Exam II November 6, 2009
I certify I have not used a programming calculator for anything other than simple mathematical
operations.
_______________________________________ (Signature)
_______________________________________ (Printed name)
Multiple-choice (24 questions, 3 pts. each) Darken the correct answer on the answer sheet.
Remember there are also 3 problems given after the multiple-choice questions. Budget
your time accordingly.
- Of the following, which are state functions?
a) H b) q e) H and E
c) w d) E
- Which of the following is true concerning enthalpy.
a) it is measured under conditions of constant volume
b) it is usually an order of magnitude larger than the internal energy of the process
c) it is an extensive property, having units of energy per mole
d) it does not depend on the state or condition of the system
e) the enthalpy change of a reaction is the reciprocal of the enthalpy change of the reverse
reaction
- 2Al(s) + 3O 2
(g) 2Al 2
O
3
(s) H° = -3351 kJ
Determine the value of H f
o for Al 2
O
3
a) -3351 kJ/mole b) -32.86 kJ/mole c) -16.43 kJ/mole d) -1676 kJ/mole
- A 1.96 g sample of titanium was burned in a bomb calorimeter that has a heat capacity of 9.
kJ/C. The temperature of the calorimeter increased from 36.84C to 98.82C. Calculate the
heat (kJ) that is released from the combustion of 1 mole of titanium.
a) 14.9 kJ/mole b) 311.2 kJ/mole
c) 609.9 kJ/mole d) 1.49 10
4 kJ/mole
e) 1.20 10
3 kJ/mole
- Consider the following reactions and their associated values of H°.
Fe 2
O
3
(s) + 3CO(g) 2Fe(s) + 3CO 2
(g) H° = -28.0 kJ
3Fe(s) + 4CO 2
(g) 4 CO(g) + Fe 3
O
4
(s) H° = +12.5 kJ
What is the value of H° for the equation shown below?
3 Fe 2 O 3 (s) + CO(g) CO 2 (g) + 2Fe 3 O 4 (s)
a) -15.5 kJ b) -59.0 kJ c) 40.5 kJ d) -109 kJ
WHITE 1 /
- Calculate the value of E for a system which performs 213 kJ of work on its surroundings and
loses 79 kJ of heat.
a) -292 kJ b) +292 kJ c) +134 kJ d) -134 kJ e) -213 kJ
- Which one of the following is not an exothermic process?
a) water evaporating b) chilling hot tea
c) making ice cubes d) condensation of water vapor
- The value of H° for the following reaction is 181 kJ. Determine the amount of heat (in kJ)
exchanged with the surroundings when 120.0 g of NO(g) is formed.
N 2 (g) + O 2 (g) 2NO(g)
a) 2.17 10
4
b) 181 c) 362 d) 724
- Cellular phones broadcast on the 33 cm band. What is the energy of this
electromagnetic radiation? (c = 3.0 x 10
8
m/s, h = 6.63 x 10
J · s.)
a) 1.7 x 10
24
J b) 6.6 x 10
J c) 6.7 x 10
J d) 6.0 x 10
J
- What is the energy change (in J) that would accompany an electronic transition from n=2 to
n=3 in a hydrogen atom? (RH = 2.18 x 10
J.)
a) 6.2 x 10
14
b) 3.0 x 10
c) - 3.0 x 10
d) 7.9 x 10
- Which of the following subshells contains only one orbital?
a) 3p b) 6f c) 5d d) 4s
- Which sketch represents an orbital that can have a principal quantum number of 3?
a) 1 b) 2 c) 4 and 5 d) 1, 2, and 3 e) all are acceptable
WHITE 2 / 4
- Rank the elements below in order of increasing atomic radius.
Be, Li, N, C, Ne
a) Be,Li,N,C,Ne b) C,N,Ne,Li,Be c) Ne,N,C,Be,Li d) Li,Be,C,N,Ne
- Which of the following elements has the most nonmetallic character?
a) F b) Si c) Se d) I
- Which one of the following traits characterizes the alkaline earth metals?
a) a very high melting point
b) existence as diatomic molecules
c) the largest atom in each period
d) the lowest I1 values of the elements in each period
e) an ns
2
valence electron configuration
- Which one of the following elements has the greatest (most exothermic) electron affinity?
a) Na b) B c) O d) K
- Which one of the elements below has the largest first ionization energy?
a) Si b) Cl c) Na d) Ar e) Mg
YOU MUST SHOW YOUR WORK ON THE ANSWER SHEET FOR THE FOLLOWING
PROBLEMS
- (8 pts.)
Substance Hf° (kJ/mol)
CO 2 (g) -
H 2 O(g) -
C 2 H 4 (g) 52
What is the value of H° for the following reaction? Is the reaction endothermic or
exothermic? Explain why.
C 2 H 4 (g) + 3O 2 (g) 2CO 2 (g) + 2H 2 O(g)
- (10 pts.) A 0.75 g portion of KCl (s) was added to 25.0 ml of water in a coffee cup
calorimeter at 24.33C. It dissolved completely and the minimum temperature reached was
22.67C. Estimate H (in kJ/mole) for the solution process. Assume the specific heat of the
solution is the same as pure water, 4.18 J/gC and the density of water is 1.0 g/ml.
- (10 pts.) Write the electron configuration for ground state Se and Tc using long hand
notation. Label both the core electrons and the valence electrons. How many unpaired
electrons are present in each?
WHITE 4 / 4
ANSWER KEY
- e 2. c 3. d
- d 5. b 6. a
- a 8. c 9. d
- b 11. d 12. e
- c 14. b 15. e
- a 17. b 18. d
- a 20. c 21. a
- e 23. c 24. d
- (8 pts.) C 2 H 4 (g) + 3O 2 (g) 2CO 2 (g) + 2H 2 O(g)
rxn f 2 f 2 f 2 4 f 2
rxn
rxn
ΔH = 2 molΔH(CO) + 2 molΔHHO - 1 molHCH H = 2 mol ΔH = 2 molΔH(CO) + 2 molΔHHO - 1 molHCH H (CO ) + 2 mol ΔH = 2 molΔH(CO) + 2 molΔHHO - 1 molHCH H H O - 1 mol H C H - 3 mol ΔH = 2 molΔH(CO) + 2 molΔHHO - 1 molHCH H (O )
ΔH = 2 molΔH(CO) + 2 molΔHHO - 1 molHCH H = 2 mol 394 + 2 mol 242 - 1 mol 52 - 3 mol 0
ΔH = 2 molΔH(CO) + 2 molΔHHO - 1 molHCH H = -1324 kJ
kJ kJ kJ kJ
mole mole mole mole
The reaction is exothermic because heat is given off during the reaction as indicated by the
negative sign.
- (10 pts.)
rxn
J
q = - 4.18 25.75g 22.67°C - 24.33°C = 178.67 J
g C
1mole KCl
0.75 g KCl = 0.01 mole KCl
74.6g
178.67 J 1 kJ
kJ = 17.
mole 0.01 mole KCl 1000 J
- (10 pts.)
Se: 1s
2 2s
2 2p
6 3s
2 3p
6 core electrons
4s
2 3d
10 4p
4 valence electrons (3d
10 should be included with the core electrons)
(4p) 2 unpaired electrons
Tc: 1s
2 2s
2 2p
6 3s
2 3p
6 4s
2 3d
10 4p
6 core electrons
5s
2 4d
5 valence electrons
(4d) 5 unpaired electrons
WHITE 5 / 4
