Please use the following constants and conversions in the problems below as needed
Planck’s constant:
h = 6.626 × 10-34 J-s
Speed of Light:
c = 3.00 × 108 m/s
Rydberg Constant:
RH = 1.10 × 107 m-1
Energy levels in hydrogen atom:
En = (-2.18 × 10-18 J)(1/n2)
1.
[7 points] Which one of the following is an exothermic process?
(a)
(b)
(c)
(d)
(e)
ice melting
water evaporating
boiling soup
condensation of water vapor
Ammonium thiocyanate and barium hydroxide are mixed at 25 °C and the
temperature drops
2. [7 points] The standard enthalpy of formation for ammonia, NH3(g), is ∆Hf° = -46.2
kJ/mol. How much heat is released/absorbed when 1 mole of N2(g) is reacted with
three moles of H2(g) to produce ammonia (at constant pressure)?
(a)
(b)
(c)
(d)
(e)
46.2 kJ of heat is released
46.2 kJ of heat is absorbed
92.4 kJ of heat is released
92.4 kJ of heat is absorbed
23.1 kJ of heat is released
3. [7 points] Consider the combustion reaction between octane and oxygen in the cylinder
of an automobile. The reaction generates CO2, H2O and heat, and at the same time the
expanding gases push up the piston thereby powering the car. If the system is defined
as the contents of the cylinder (not including the piston or the cylinder) which of the
following statements is true for the system in this process?
(a)
(b)
(c)
(d)
The change in internal energy (∆E) is negative
The change in internal energy (∆E) is positive
The change in internal energy (∆E) is zero
Not enough information is given to unambiguously determine the sign of ∆E
4. [7 points] Which one of the following statements is true?
(a) Enthalpy is an intensive property
(b) The enthalphy change for a reaction does not depend upon the state (solid, liquid,
gas, aqueous) of the reactants and products
(c) Enthalpy is a state function
(d) Enthalpy is equal to the heat measured under conditions of constant volume
(e) If the enthalpy change of a reaction is ∆Hrxn the reverse reaction will have an
enthalpy change equal 1/∆Hrxn
5. [7 points] Given the following standard enthalpies of formation:
Br2 (l)
Br2 (g)
Br (g)
→
→
→
∆Hf° = 0 kJ/mol
∆Hf° = 30.7 kJ/mol
∆Hf° = 112 kJ/mol
Which of the following statements is false?
(a)
(b)
(c)
(d)
(e)
Bromine is a liquid in it’s standard state
The formation of Br2(g) from gas phase bromine atoms is endothermic
The evaporation (liquid → gas) of bromine is endothermic
The condensation (gas → liquid) of bromine is exothermic
Pick this answer if all of the above statements are true.
6. [7 points] If 25.0 g of sodium peroxide (Na2O2, MW = 78.0 g/mol) is reacted with 12.1
g of water (H2O, MW = 18.0 g/mol) according to the following thermochemical equation:
2Na2O2(s) + 2H2O(l) → 4NaOH(s) + O2(g)
∆H = -126 kJ
What quantity of heat is released (assuming the pressure is held constant)?
(a)
(b)
(c)
(d)
(e)
-20.2 kJ
-40.4 kJ
-42.4 kJ
-84.7 kJ
-126 kJ
7. [7 points] As an experiment you add a 155 g piece of aluminum (specific heat, Cs = 0.90
J/g-K) and a 165 g piece of lead (specific heat, Cs = 0.13 J/g-K) to a beaker of boiling
water. After a few minutes both pieces of metal come to the same temperature as the
water (100 °C). Next you take both pieces of metal out of the water and set them on the
benchtop. After 5 minutes you measure the temperature of each piece of metal. Assuming
both pieces of metal lose heat at the same rate which of the following statements is true?
(a)
(b)
(c)
(d)
The lead will be cooler than the aluminum
The aluminum will be cooler than the lead
Both pieces of metal will be at the same temperature
There is not enough information given to know whether the lead or the aluminum
will be cooler
8. [7 points] Given the following reactions
Fe2O3 (s) + 3CO (g) → 2Fe (s) + 3CO2 (g)
3Fe (s) + 4CO2 (g) → 4CO (g) + Fe3O4 (s)
∆H = -28.0 kJ
∆H = +12.5 kJ
What is ∆Hrxn for the following reaction?
3 Fe2O3 (s) + CO (g) → CO2 (g) + 2 Fe3O4 (s)
(a) +109 kJ
(b) -109 kJ
(c) –15.5 kJ
(d) +40.5 kJ
(e) -59 kJ
9. [7 points] Given the following standard enthalpies of formation:
Compound
PCl3(g)
HCl(g)
PH3(g)
∆Hf° (kJ/mol)
-288.07
-92.30
+5.40
What is ∆H° for the following reaction:
PCl3(g) + 3HCl(g) → 3Cl2(g) + PH3(g)
a.
b.
c.
d.
e.
∆Hrxn = -570.37 kJ
∆Hrxn = -385.77 kJ
∆Hrxn = +570.37 kJ
∆Hrxn = +385.77 kJ
The ∆Hf° of Cl2(g) is needed to complete the calculation.
10. [7 points] Acid-base neutralization reactions are typically exothermic. Because of
this solutions can get quite hot when carrying out neutralization reactions. Given the
following standard enthalpies of formation:
Compound
∆Hf° (kJ/mol)
Compound
∆Hf° (kJ/mol)
HCl (aq)
NaOH (aq)
-167
-470
H2O (l)
NaCl (aq)
-288
-407
Calculate ∆H° for the following neutralization reaction:
NaOH(aq) + HCl(aq) → H2O(l) + NaCl(aq)
(a)
(b)
(c)
(d)
(e)
∆Hrxn = +58 kJ
∆Hrxn = -1332 kJ
∆Hrxn = +1332 kJ
∆Hrxn = -58 kJ
None of the above answers is correct.
11. [7 points] 250.0 mL of 6.0 M sodium hydroxide solution is mixed with 250.0 mL of 6.0
M hydrochloric acid solution in a calorimeter. What is the final temperature of the
mixture if both solutions are at a temperature of 25.0 °C before mixing? The density of
the resulting solution is 1.02 g/mL and the specific heat is 4.18 J/g-K. Assume the
calorimeter is perfect and no heat is lost to the surroundings.
(a)
(b)
(c)
(d)
(e)
–15.8 °C
83.0 °C
58.0 °C
40.8 °C
65.8 °C
12. [7 points] The standard enthalpies of formation, ∆Hf°, for CCl4(l) and CH4(g) are
-139.3 kJ and -74.8 kJ respectively, and the heat of vaporization of carbon tetrachloride
is endothermic by 32.6 kJ/mol, as shown in the equation below:
CCl4(l) → CCl4(g)
∆H°rxn = +32.6 kJ
Given this information calculate the enthalpy of the following reaction?
CH4(g) + 2Cl2(g) → CCl4(g) + 2H2(g)
(a)
(b)
(c)
(d)
(e)
-64.5 kJ
–31.9 kJ
–97.1 kJ
+64.5 kJ
+97.1 kJ
13. [7 points] What is the wavelength of light that has a frequency of 1.20 x 1013 Hz ?
(a) 25.0 m
(b) 2.50 × 10-5 m
(d) 12.0 m
(e) 4.00 × 10-4 m
(c) 4.00 × 104 m
14. [7 points] What is the wavelength of a photon that has an energy of 5.25 x 10-19 J ?
(a) 3.79 × 10-7 m
(b) 2.64 × 106 m
(d) 4.21 × 10-24 m
(e) 37,900,000 m
(c) 2.38 × 1023 m
15. [7 points] Which of the following colors of light has the lowest energy photons?
(a) green
(b) violet
(c) blue
(d) red
(e) yellow
16. [7 points] Einstein was able to explain the photoelectric effect by proposing that
light behaves in some ways as a particle called a photon? For sodium metal it is known that
only photons with energies equal to or greater than 4.41 × 10-19 J are capable of ejecting
electrons. Given this information which group of photons will be capable of ejecting one or
more electrons from sodium?
(a)
(b)
(c)
(d)
(e)
Five photons each with an energy of 1.00 × 10-19 J
Two photons each with a wavelength of 410 nm
Two photons each with a wavelength of 550 nm
Both (a) and (b)
All three (a), (b) and (c)
17. [7 points] Which of the following electronic transitions in a hydrogen atom lead to
the emission of a photon with the shortest wavelength?
(a)
(b)
(c)
(d)
(e)
n=2
n=3
n=4
n=5
n=5
→
→
→
→
→
n=1
n=2
n=3
n=4
n=1
18. [7 points] The n = 2 to n = 6 transition in the Bohr hydrogen atom corresponds to the
__________ of a photon with a wavelength of __________ .
(a) emission, 411 nm
(b) absorption, 411 nm
(c) absorption, 657 nm
(d) emission, 93.8 nm
(e) emission, 389 nm
19. [7 points] According to the Heisenberg Uncertainty Principle, it is impossible to know
precisely both the position and the __________ of an electron.
(a) mass
(b) color
(c) momentum
(d) shape
(e) wavelength
20. [7 points] Which quantum number defines the shape of an orbital?
(a) principle, n
(b) azimuthal, l
(c) magnetic, ml
(d) spin, ms
(e) all orbitals have the same shape
21. [7 points] Which of the following electron configurations is correct for bromine?
(a)
(b)
(c)
(d)
(e)
[Ar] 4s24p5
[Ar] 4s24d104p5
[Ar] 4s23d104p5
[Kr] 4s24d104p5
[Kr] 4s23d104p5
22. [7 points] How many unpaired electrons are there in a sulfur atom?
(a) 1
(b) 2
(c) 3
(d) 4
(e) 6
23. [7 points] How many electrons in a cadmium (Cd) atom have a magnetic quantum
number, ml, equal to 2?
(a) 0
(b) 2
(c) 4
(d) 10
(e) 20
24. [7 points] Which of the following statements concerning nodes is false?
(a) A node is where the electron wavefunction (ψ) changes sign
(b) The probability of finding an electron at a node is zero
(c) For a given orbital the number of nodal planes is equal to the azimuthal quantum
number, l
(d) All orbitals have at least one node
(e) A 3p orbital has one radial node and one nodal plane
25. [7 points] Among the following sets of quantum numbers which set does not
correspond to an electron in a zinc atom (in it’s ground state)?
(a) n = 4, l = 0, ml = 0, ms = +½
(b) n = 3, l = 0, ml = 0, ms = +½
(c) n = 3, l = 2, ml = -2, ms = -½
(d) n = 4, l = 2, ml = 2, ms = -½
(e) n = 2, l = 1, ml = -1, ms = -½