CHEMISTRY II
PRACTICE PROBLEMS FOR 2ND SEMESTER FINAL
2008-2009
This is just a sample of problems to refresh your memory. You have many problem sets
that we worked throughout each of the chapters that you can use to study as well. There
are many questions in the textbook that you can work for extra practice (remember, the
numbers in blue have answers in the back of the book).
CHAPTER 5:
1.
Nitrogen gas reacts with hydrogen gas to produce gaseous ammonia
a.
What is the maximum mass of ammonia that can be produced from a
mixture of 1.00 X 103 grams of nitrogen and 5.00 X 102 grams of
hydrogen?
b.
What mass of excess reactant will remain unreacted?
2.
Describe how you would prepare 250.0 mL of a 0.20 M NaIO3 solution from a
10.0 M NaIO3 stock solution.
3.
A flexible weather balloon contains helium gas at a volume of 855 L. Initially, the
balloon is at sea level, where the temperature is 25oC and the barometric pressure
is 720. torr. The balloon then rises to an altitude of 6000 feet, where the pressure
is 605 torr and the temperature is 15oC. What is the volume of the balloon at 6000
feet?
4.
A 5.0 L flask contains 0.60 grams of oxygen gas at a temperature of 22oC. What
is the pressure (in kPa) inside the flask?
5.
Calculate the volume of oxygen gas, at STP, required for the complete
combustion of 125 grams of octane (C8H18) to carbon dioxide and water.
6.
A mixture of 1.00 grams of hydrogen gas and 2.50 grams of helium is placed in a
2.50 L container at 27oC. Calculate the partial pressure of each gas and the total
pressure of the container.
7.
A gas consisting of only carbon and hydrogen has an empirical formula of CH2.
The gas has a density of 1.65 g/L at 27oC and 734 torr. Determine the molar mass
and molecular formula of the gas.
8.
A sample of nitrogen gas was collected over water at 20.oC and a total pressure of
1.00 atm. A total volume of 2.50 X 102mL was collected. What mass of nitrogen
was collected? (At 20.oC the vapor pressure of water is 17.5 torr)
CHAPTERS 6 & 16:
1.
Calculate ∆H for the following reaction using Hess’s law:
C2H4(g) + 6F2(g) --- 2CF(g) + 4HF(g)
Given the following:
H2(g) + F2(g) ---- 2HF(g)
∆H = -537 kJ
C(s) + 2F2(g) ---- CF(g)
∆H = -680. kJ
2C(s) + 2H2(g) ---- C2H4(g)
∆H = +52.3 kJ
2.
3.
4.
When a student mixes together 250.0 mL of 1.00 M HCl and 250.0 mL of 1.00 M
NaOH in a “coffee cup” calorimeter, the temperature of the resultant solution
increases from 25.0°C to 28.3°C. Assuming that the calorimeter absorbs only
negligible quantity of heat, the density of the solution is 1.00 g/mL and the
specific heat capacity is the same as liquid water, calculate the enthalpy change
per mole for the reaction.
A 25.62 gram sample of metal is heated to 98.6°C and is placed in a “coffee cup”
calorimeter that initially contains 45.00 grams of water at 22.3°C. If the final
temperature is 28.9°C, what is the specific heat capacity of the metal?
How much heat is produced when 4.50 grams of methane gas is burned in a
constant-pressure system?
CH4(g) + 2O2(g) --- CO2(g) + 2H2O(g) ∆H = -802 kJ
5.
A reaction between hydrogen and oxygen gases occurs. The system loses 550 J of
heat to its surroundings. The expanding gases do 240 J of work on the
surroundings. What is the change in internal energy of the system?
6.
Calculate ∆H for the following reaction:
2C3H6(g) + 9 O2(g) --- 6CO2(g) + 6H2O(l)
(Questions 7-9) Determine whether each of the following involves an increase or
decrease in the entropy of the system:
7.
ice melting
8.
2N2O5(g) -- 4NO2(g) + O2(g)
9.
2LiOH(aq) + CO2(g) --- Li2CO3(aq) + H2O(l)
10.
Using data for ∆H° and ∆S°, calculate ∆G° for the following reaction at 25°C and
1 atm.
C3H8(g) + 5O2(g) --- 3CO2(g) + 4H2O(g)
CHAPTER 7:
1.
Calculate the energy (per photon) of radiation that has a frequency of 6.0 X 1013
Hz.
2.
Calculate the wavelength associated with a 750 kg automobile traveling at 80.0
km/hr.
3.
What does it mean to say that something is quantized?
4.
Calculate the wavelength associated with a spectral line occurring at 25.0 cm
within a spectroscope (shirtbox) that is 42.0 cm in length.
5.
Calculate the wavelength (in nm) associated with an electron moving from the 4th
to the 2nd energy level of the hydrogen atom. Also, does it emit or absorb photons
when this occurs?
6.
Which color of the visible spectrum has the lowest frequency, longest
wavelength, and lowest energy?
7.
A laser emits a light with a frequency of 1.50 X 1014 Hz. Calculate the energy per
mole of photons that is emitted.
8.
Does the energy of a photon increase or decrease with decreasing wavelength?
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
Describe Bohr’s model of the atom. State why it is no longer accepted. Compare
and contrast Bohr’s model to the wave mechanical model of the atom.
Determine if the following sets of quantum numbers are allowed. For the sets that
are not correct, state what is wrong with it.
a.
n = 3, l = 3, ml = -1, ms = +1/2
b.
n = 4, l = 2, ml = 0, ms = -1/2
Place the following atoms in order of decreasing atomic radius:
Cs, F, K, P, I Xe
Which of the following would have the least exothermic electron affinity: Mg, Si,
Cl
Which of the following would have the lowest first ionization energy: Pb, S
Arrange the following in order of increasing electronegativity: S, I, Po
Write the electron configuration and orbital diagram for the following elements.
You may use the shorthand notation if there are more than 20 electrons in the
atom:
a.
Mo
b.
Am
c.
Os
d.
P
Determine the number of valence electrons in the following:
a.
I
b.
As
c.
Ca
d.
Cs
Determine the number of unpaired electrons in the following:
a.
Bi
b.
Gd
c.
Ni
d.
Xe
How many electrons in an atom can have the quantum numbers n = 4, l = 2?
CHAPTER 8:
1.
Draw a figure indicating the direction of the dipole moment including which end
of the bond is negative and which is positive for S-Cl.
2.
Use bond energy values to determine ∆H for the following reaction:
H H
CH2-CH2 + HCN ------
O
3.
HOC-C-C=N
H H
Draw the Lewis dot structure for the following and then determine the geometric
shape and bond angle(s) for the following:
a.
ClO3b.
OF2
c.
BH3
4.
5.
6.
d.
SO3
e.
BrF3
Draw the Lewis structure and resonance structure(s) (if any) for the carbonate
polyatomic ion:
Order the following ions from smallest to largest: Br-, F-, At-, Cl-, IDetermine if NH3 has a dipole moment. If it does, show it using the arrow
method.
ANSWERS
ANSWERS TO CHAPTER 5:
1.
a.
1.22 X 103 g ammonia
b.
284 grams of excess reactant
2.
Take 5.0 mL of the 10.0 M stock solution and add enough water to make 250.0
mL of total solution
3.
983 L
4.
9.3 kPa
5.
306 L oxygen
6.
PH2 = 4.88 atm; PHe = 6.15 atm; Ptotal = 11.03 atm
7.
molar mass = 42.0 g/mol; molecular formula = C3H6
8.
0.29 g nitrogen
CHAPTERS 6 & 16:
1.
-2486 kJ
2.
-28,000 J/mol
3.
0.67 J/goC
4.
-225 kJ
5.
-790 J
6.
-4119 kJ
7.
increase (going from solid to liquid)
8.
increase (2 gas to 5 gas molecules)
9.
decrease (2 aqueous + 1 gas to 1 aqueous + 1 liquid)
10.
-2080 kJ
CHAPTER 7:
1.
4.0 X 10-20 J
2.
4.0 X 10-38 m
3.
it occurs in set, specific amounts
4.
1130 nm
5.
479.0 nm, emit
6.
red
7.
5.99 X 104 J/mol
8.
increase – if wavelength gets shorter, frequency goes up and energy increases
9.
a.
Model: electrons orbit the nucleus in a set, circular path; it takes a set
amount of energy to move the electron among energy levels.
b.
10.
11.
12.
13.
14.
15.
16.
17.
18.
Wrong with Bohr’s: electrons don’t move in circular orbits, and it
only worked for hydrogen.
c.
Both models attempt to describe the model of the atom. The wave
mechanical model has the electrons moving in a standing wave pattern,
not circular paths like Bohr’s model.
a.
not possible, l can’t equal 3 when n = 3 (l must be 0, 1, or 2)
b.
possible
Cs, I, Xe, K, P, F
Mg
Pb
Po, I, S
[Kr]5s24d4
[Rn]7s25f66d1
[Xe]6s24f145d6
1s22s22p63s23p3
a.
7
b.
5
c.
2
d.
1
a.
3
b.
8
c.
2
d.
0
10
CHAPTER 8:
1.
S—Cl
+--
2.
-43 kJ
3.
a.
trigonal pyramidal, <109.50
b.
bent, <109.5o
c.
trigonal planar, 120o
d.
trigonal planar, 120o
e.
T-shaped, 90o and 120o
4.
come check this one with me
5.
F-, Cl-, Br-, I-, At6.
it does have a dipole moment (0.9 = polar). Arrow end should point toward
the nitrogen