KING FAHD UNIVERSITY OF PETROLEUM AND MINERALS

 
CHEM-102-061-First-Major EXAM


Important constants
Gas Constant (R)
= 0.0821
= 8.31
= 8.31 x 107
L.atm/(mol.K)
J/(mol.K)
g.cm2/(sec2.mol.K)
Planck’s Constant (h)
= 6.626 x 10-34
= 6.626 x 10-34
J.sec/particle kg.m2/(sec.particle)
Velocity of light (c)
= 2.998 x 108
m/sec
Avogadro’s number (N)
= 6.022 x 1023
particles/mole
Bohr’s Constant (RH)
= 2.179 x 10-18
J/particle
Faraday (F)
= 96485
Coulombs
Specific heat of H2O
= 4.18
J/(g.oC)



1.
For the reaction:

                           A   +   2B   →   C

doubling the concentration of B increases the rate of formation of C four times
while doubling the concentration of A has no effect on the rate of formation of
C. The rate R for formation of C is given by:
A.
R = k [B]2
B.
R = k [A]
C.
R = k[A] [B]2
D.
R = k [A] [B]4
E.
R = k [A] [B]


2.
A first order reaction of the type

               aA   →   products

has a half life, t1/2, of 138.6 s. The time needed for the A concentration to drop
20 % from its initial value is:
A.
44.6 s
B.
444   s
C.
111   s
D.
322   s
E.
32.0 s


3.
The activation energy is:
A.
the minimum energy needed for a reaction to occur.
B.
not required for exothermic reactions.
C.
the heat of reaction of endothermic reactions.
D.
the energy that is converted into kinetic energy during a chemical reaction.
E.
the difference between the energies of reactants and products.


4.
At 45 °C dinitrogen pentoxide (N2O5), dissolved in chloroform, undergoes
the following first order decomposition,
 
                               2N2O5 (g)    →    4NO2 (g)    +    O2 (g)
 
with a rate constant of 6.20 x 10 4 min 1 . What is the rate of formation of
nitrogen dioxide when [N2O5] = 0.40 M.
A.
4.96 x 10 4 M min 1.
B.
6.20 x 10 4 M min 1.
C.
2.48 x 10 4 M min 1.
D.
3.10 x 10 4 M min 1.
E.
1.24 x 10 4 M min 1.


5.
The reaction    
                                             aA   →   products

is first order with a rate constant of 1.68 x 10 2 s1 at 25 °C.   2.50 mol of A
are placed in a 5.0 L container maintained at 25 °C. How many moles of A
remain after 1.0 minutes?    
A.
0.91
B.
0.18
C.
1.0
D.
0.69
E.
0.50


6.
For the reaction,
 
                         2A (g)    +    B (g)   ⇌   C (g)
 
the initial amounts in a 1.0-L flask were 1.80 mol of A and 0.90 mol of B.
At equilibrium the amount of A was 1.20 mol. The equilibrium constant
for this reaction is:
A.
0.35
B.
1.4
C.
0.42
D.
1.7
E.
0.83


7.
For the reaction,

                       A2 (g)   +   2B2 (g) ⇌ A2B4 (g)     ,     ΔH = –85 kJ

the equilibrium constant is increased by,
A.
decreasing the temperature.
B.
increasing the temperature.
C.
adding a catalyst.
D.
adding A2.
E.
decreasing the volume.


8.
For the reaction

                                    2A (g) ⇌   B (g)   +   C (g)

Kp is 64.0 at 400 °C. Starting with A at 3.00 atm., what is the total pressure
when the system reaches equilibrium at 400 °C?
A.
3.00 atm
B.
5.67 atm
C.
2.67 atm
D.
2.88 atm
E.
4.41 atm


9.
An equilibrium mixture for the reaction

                                        Br2 (g)   +   Cl2 (g)   ⇌   2BrCl (g)

contains 1.40 mol Br2 (g), 0.200 mol Cl2 (g) and 1.40 mol BrCl (g) in a 2.00-L
flask. If 1.20 mol Cl2 are added to this mixture what would the concentration
of Cl2 be after the system is allowed to return to equilibrium at the same
temperature?
A.
0.452 M
B.
0.248 M
C.
0.205 M
D.
0.495 M
E.
0.904 M


10.
Which of the following reactions has the least tendency to go to completion?
A.
N2 (g)   +   O2 (g)   ⇌   2 NO (g)      Kc = 5.0 x 10 31
B.
2 H2 (g)   +   O2 (g)   ⇌   2 H2O (g)      Kc = 1.7 x 10 27
C.
H2 (g)   +   Cl2 (g)   ⇌   2 HCl (g)       Kc = 3.2 x 10 16
D.
2 HF (g) ⇌   H2 (g)   +   F2 (g)      Kc = 1.0 x 10 13
E.
2 NOCl (g)   ⇌   2 NO (g)   +   Cl2 (g)   Kc = 4.7 x 10 4



11.
Which of the following pairs is not a conjugate acid-base pair?
A.
H30 + / OH
B.
NH4 + / NH3
C.
HCO3 / CO3 2–
D.
HC2H3O2 / C2H3O2
E.
HCl / Cl


12.
A 0.0445 M solution of a weak base B

      B(aq)   +   H2O (liq)   ⇌ BH + (aq)   +    OH (aq)

has a pH of 10.32. What is the ionization constant, Kb, of the weak base?
A.
9.81 x 10 7
B.
214
C.
4.29 x 10 8
D.
9.57 x 10 6
E.
4.67 x 10 3


13.
What is the pH of a 0.125 M aqueous solution of sodium acetate (C2H3O2Na)
given that the dissociation constant, Ka, for acetic acid (C2H3O2H) is 3.78 x 10 7?
A.
9.76
B.
4.24
C.
3.51
D.
6.42
E.
17.7


14.
A 1.00 M solution of a weak monoprotic acid (HB) dissociates 1.5 % .
What is the percent dissociation of a 0.25 M solution of this acid?
A.
3.0 %
B.
9.0 %
C.
3.8 %
D.
1.7 %
E.
6.0 %


15.
What is the concentration of CO3 2– in a 0.010 M solution of carbonic acid
(H2CO3)? The equilibria are given below:

   H2CO3 (aq)    ⇌   H + (aq)   +   HCO3 (aq)      ;      Ka1 = 4.3 x 10 7
   HCO3 (aq)   ⇌   H + (aq)   +   CO3 2– (aq)        ;      Ka2 = 5.6 x 10 11
A.
5.6 x 10 11 M
B.
6.7 x 10 11 M
C.
6.6 x 10 1 M
D.
3.9 x 10 7 M
E.
7.5 x 10 7 M


16.
The Lewis acid-base model states that a base
A.
donates a pair of electrons.
B.
accepts a pair of electrons.
C.
accepts a hydroxyl ion.
D.
reacts with the solvent to form cations.
E.
must have a hydroxyl ion.


17.
What is the pH of the solution obtained by mixing 50.0-mL of 0.100 M HCl
and 150.0-mL of 0.100 M NH3? For NH3 Kb = 1.8 x 10 5.
A.
9.26
B.
10.26
C.
8.96
D.
10.98
E.
4.44


18.
0.500-L of a 0.200 M AgNO3 solution is mixed with 0.500-L of a 4.00 M NH3
solution. Given that the formation constant of the complex ion [Ag(NH3)2]+
is 2.0 x 10 7 calculate the concentration of Ag+ ions in solution?
A.
1.5 x 10 9 mol/L
B.
1.3 x 10 9 mol/L
C.
2.0 x 10 9 mol/L
D.
6.0 x 10 9 mol/L
E.
2.8 x 10 9 mol/L


19.
In a buffer of pH = 6.3 the concentration of the conjugate base is double
the concentration of the acid. Ka of the acid is:
A.
1.0 x 10 6
B.
1.0 x 10 4
C.
1.0 x 10 8
D.
5.0 x 10 7
E.
1.0 x 10 12


20.
In a solution that is 0.10 M in each of Fe2+, Cu2+ and Cd2+ the sulfide ion (S2–)
concentration was adjusted to 1.0 x 10 20 M. Given that:

Ksp (CdS) = 8.0 x 10 27
Ksp (CuS) = 6.3 x 10 36
Ksp (FeS)   = 6.3 x 10 18

which of the sulfides will precipitate?
A.
CdS and CuS.
B.
CuS only.
C.
CuS and FeS.
D.
FeS only.
E.
All three sulfides.



STOP This is the end of the test. When you have completed all the questions and reviewed your answers, press the button below to grade the test.