Practice Exam I (Tro chapters 10, 11, 13)
Dr. Overway
CHEM 162
Here are some things you may need.
Formal Charge = # of valence e - - # of non-bonding e - - # of bonds
Formal Charge = # of valence e - - # of non-bonding e - - ½ (# of bonding e - )
R= 8.3145 J/(K mol)
R=0.08206 (Latm)/(Kmol)
Psolv = Xsolv Posolv
Kb (water) = 0.512 C kg/mol
Kf (water) = 1.858 C kg/mol
T = Kf cm ·i
T = Kb cm ·i
= MRT·I
𝑙𝑛[A] = 𝑙𝑛[𝐴]0 − 𝑘𝑡
𝑘
𝑅 𝑙𝑛 ( 2 )
𝑘1
𝐸𝑎 =
1
1
−
𝑇1 𝑇2
𝐸 1 1
𝑘2
[ 𝑎 ( − )]
= 𝑒 𝑅 𝑇1 𝑇2
𝑘1
E=hc/λ
h=6.62610-34 Js
𝑡1/2 =
c=2.9979108 m/s
Avogadro’s number = 6.022×1023 things/mol
𝑡1/2 =
1
𝑙𝑛 (2)
−𝑘
1
𝑘[A]0
−𝐸𝑎
𝑘 = 𝐴𝑒 𝑅𝑇
1
1
=
+ 𝑘𝑡
[A] [A]0
𝐸𝑎 1
ln 𝑘 = ln 𝐴 − ( ) ( )
𝑅 𝑇
CHEM 162
Practice Exam
1. Match each of the following terms with the correct definitions.
Answer Term
Definition
polymorph
A a highly ordered solid
allotrope
B a solid substance whose molecules are held together by covalent
bonds
ionic solid
C a solid substance whose molecules are held together by metallic
bonds
network covalent solid D the different crystal structures in which an element can exist
metallic solid
E a crystal structure the containing an atom at each of the corners of
the cube and an atom at each face of the cube
molecular solid
F a solid substance whose molecules are held together by ionic
bonds
crystalline solid
G a substance that has very little order
amorphous solid
H a substance that bursts into flame when in contact with the air
I the different crystal structures in which a compound can exist
J a solid substance whose molecules are held together by H-bonds,
dipole-dipole forces, or dispersion forces
2. In each of the following comparisons, circle the correct compound.
highest boiling point:
CH4
CH3CH2OH
lowest viscosity:
H2O
CH3CH2CH3
highest vapor pressure at 25 C:
PH3
NH3
highest boiling point:
H2S
H2O
lowest freezing point:
SF6
CH3CH2CH2CH2CH3
3. Determine whether each of the following statements are true (T) or false
(F) concerning the two phase diagrams shown below.
Substance C is less dense as a liquid than a solid.
At pt. 1 substance D is a supercritical fluid.
Going from pt. 2 to pt. 3 in the phase diagram for substance D involves a
phase change from gas to solid.
At 1 atm of pressure substance D melts and substance C sublimes if the
temperature is increased.
4. Of the intermolecular forces listed in the textbox to the right, which would be the strongest force that
would have to be overcome in order to convert the following molecules from a liquid to a gas?
a. CCl4
______________________________.
A) Ionic
b. HBr
______________________________.
B) Covalent
C) Dispersion
c. H2O
______________________________.
D) Dipolar
d. H2NCH2CH2CH3
______________________________.
E) Metallic
e. CH3CH2CH2CH3
F) Hydrogen bonding
______________________________.
5. Circle the aqueous solution that should have the highest boiling point. Explain your answer.
A.
1.0 M KNO3 (electrolyte)
B.
0.75 M NaCl (electrolyte)
C.
0.75 M CuCl2 (electrolyte)
D.
2.0 M C12H22O11 (sucrose, non-electrolyte)
6. (8 pts) Dimethylglyoxime, DMG, is an organic compound used to test for aqueous nickel(II) ions. A
solution prepared by dissolving 65.0 g of DMG (a non-electrolyte) in 375 g of ethanol boils at
80.3°C. What is the molar mass of DMG? (Kb = 1.22 C /molal, boiling point of pure ethanol =
78.5°C)
7. Lysine is an amino acid that is an essential part of nutrition but which is not synthesized by the
human body. What is the molar mass of lysine if 750.0 mL of a solution containing 8.60 g of lysine
(a non-electrolyte) has an osmotic pressure of 1.918 atm? (T = 25.0°C)
8. Draw the band gap structure for 1) an insulator and 2) a conductor. Label all of the parts.
9. Given a Rate Law of Rate=k[A]2[B]1, if you wanted to increase the rate of the reaction in the most
efficient way, which chemical would you increase in concentration knowing that both A and B are
very expensive? Explain.
2 N2O5 (g)  4 NO2 (g) + O2 (g)
10. The following data was measured for the reaction:
Time (s)
[N2O5] (M)
0
0.100
50.0
0.0707
100.0
0.0500
From the above data, the following graphs were made:
A) Write the rate law for the reaction
B) Calculate the rate constant (k) and provide the correct units.
C) Propose a mechanism that is consistent with the rate law
200.0
0.0250
300.0
0.0125
400.0
0.00625
11. Radioactive materials, such as 60Co, are often used in biological studies. A radiation biologist
studied the rate of decomposition of 60Co and obtains the following data:
Time (min)
0
30.0
60.0
90.0
180.0
60
Co (µg)
15.4
11.66
8.84
6.69
2.91
A) What reaction order do nuclear reactions follow?
B) Determine the rate constant with proper units.
C) Determine the half-life of 60Co.
12. True/False (T or F)
The slowest step in a mechanism has the smallest activation energy (Ea)
The solid catalyst in an exhaust system of a car is a heterogeneous catalyst
As the activation energy (Ea) decreases, the rate (speed) of a reaction decreases
Transition states (activated complexes) are fairly stable and can be found in the valleys of a
reaction diagram
If the equilibrium constant (Keq ) of a reaction is large, the reaction is very fast
If the rate constant (k) of a reaction is large, the reaction is very fast
13. Determine the rate law for each of the following overall reactions:
A) C2H4 (g) + Br2 (g)  C2H4Br2 (g)
Rate = ____________________
B) 2 ClO2 (aq) + 2 OH-(aq)  ClO3-(aq) + ClO2-(aq) + H2O (l) Rate = ____________________
14. For the overall reaction of C2H4 (g) + H2 (g)  C2H6 (g) , draw a reaction diagram for the uncatalyzed
and catalyzed reactions - that makes two reaction paths on the same chart. Label the E, the
activation energy (Ea), reaction intermediate(s), and the transitions state(s), axes labels, reactants,
products.
uncatalyzed reaction:
step 1: C2H4 (g) + H2 (g)  C2H6 (g)
Ea uncat = 200 kJ/mol
Erxn uncat = + 60 kJ/mol
catalyzed reaction:
step 1 (slow):
C2H4 (g) + Pd(s)  C2H4Pd (ad)
Ea cat 1 = 80 kJ/mol
Erxn cat1 = + 30 kJ/mol
step 2 (fast): C2H4Pd (ad) + H2 (g)  C2H6 (g) + Pd(s)
Ea cat 2 = 40 kJ/mol
Erxn cat 2 = + 30 kJ/mol
15. Write the Rate Law for the following mechanisms
A) step 1:
step 2:
NO2 (g) + F2 (g)  NO2F(g) + F(g)
NO2(g) + F(g)  NO2F(g)
fast
slow
Rate Law = ______________________________
B) step 1:
step 2:
NO2 (g) + F2(g)  NO2F(g) + F(g)
NO2(g) + F(g)  NO2F(g)
slow
fast
Rate Law = ______________________________
C) step 1:
step 2:
F2(g)  F(g) + F(g)
2 NO2(g) + 2 F(g)  2 NO2F(g)
slow
fast
Rate Law = ______________________________
16. For the reaction: H2O2 (aq) + 3 I-(aq) + 2 H+(aq)  I3- (aq) + 2 H2O(l)
The following initial rate data were obtained:
Initial Concentrations
Exp. # [H2O2] (M) [I-] (M) [H+] (M)
Initial Rate (M/sec)
1
0.010
0.010
0.00050
1.1510-6
2
0.020
0.010
0.00050
2.3010-6
3
0.010
0.020
0.00050
2.3010-6
4
0.010
0.010
0.00100
1.1510-6
Write the specific rate law for the reaction.
What is the rate constant k (with proper units)?
18. Answer True (T) or False (F) for the statements below.
___
a catalyst increases the activation energy of a reaction
___
a catalyst decreases the equilibrium constant (Keq) of a reaction
___
a catalyst appears in the overall chemical reaction
___
the solid catalytic converter of an automobile that converts NO(g) and CO(g) to N2 (g) and CO2 (g) is
a homogeneous catalyst
19. List two ways in which a reaction rate can be affected. Provide specific detail and give an example
(for example: if you increase the __, the reaction rate will increase (or decrease) because...)