KING FAHD UNIVERSITY OF PETROLEUM AND MINERALS

 
CHEM-102-071-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.
Consider the reaction 2H2 + O2 → 2H2O
What is the ratio of the initial rate of the appearance of water to the initial rate of disappearance of oxygen?
A.
1 : 1
B.
2 : 1
C.
1 : 2
D.
2 : 2
E.
3 : 2


2.
The following data were obtained at 55°C for the reaction,

A(aq) + B(aq) → Products.
 
[A]0
[B]0
Inital Rate
Exp.
(mol/L)
(mol/L)
(mol/L.s)
1
0.10
0.10
1.0 × 10-3
2
0.20
0.10
2.0 × 10-3
3
0.10
0.20
1.0 × 10-3
4
0.30
0.20
?

What will the initial rate (in mol/L ⋅ s) be in Experiment 4 at 55°C?
A.
3.0 × 10–3
B.
6.0 × 10–3
C.
9.0 × 10–3
D.
18 × 10–3
E.
none of the values given in the other choices.


3.
The rate law for the reaction,

          H2O2 + 3I - + 2H + → I3 - + 2H2O

is found to be,

          rate = k[H2O2][I -]

Examine mechanisms I. and II. below then select the correct
answer from the choices given.



A.
Mechanism I with the first step rate determining..
B.
Mechanism I with the second step rate determining.
C.
Mechanism II with the first step rate determining.
D.
Mechanism II with the second step rate determining.
E.
None of the other choices could be correct.


4.
If for the chemical reaction system described by the diagram below,


Ea for the forward reaction is 25 kJ/mol and the enthalpy of reaction is –95 kJ/mol, what is Ea for the reverse reaction?
A.
120 kJ/mol
B.
70 kJ/mol
C.
95 kJ/mol
D.
25 kJ/mol
E.
–70 kJ/mol


5.
The isomerization of cyclopropane follows first order kinetics. The rate constant at 700.0 K is 6.20 × 10–4 min–1, and the half-life at 760.0 K is 29.0 min. Calculate the activation energy for this reaction.
A.
5.07 kJ/mol
B.
27.0 kJ/mol
C.
50.7 kJ/mol
D.
160. kJ/mol
E.
269. kJ/mol


6.
Which one of the following choices is the correct equilibrium constant
expression for the reaction?

Fe2O3(s) + 3H2(g) 2Fe(s) + 3H2O(g)
A.
Kc = [Fe2O3] [H2]3 / [Fe]2[H2O]3
B.
Kc = [H2] / [H2O]
C.
Kc = [H2O]3 / [H2]3
D.
Kc = [Fe]2[H2O]3 / [Fe2O3] [H2]3
E.
Kc = [Fe] [H2O] / [Fe2O3] [H2]


7.
Kp for the reaction of SO2(g) with O2 to produce SO3(g) is 3 × 1024 . Calculate Kc for this equilibrium at 25ºC. (The relevant reaction is 2SO2(g) + O2(g) 2SO3(g).)
A.
3 × 1024
B.
5 × 1021
C.
2 × 1020
D.
5 × 1022
E.
7 × 1025


8.
2.50 mol NOCl was placed in a 2.50 L reaction vessel at 400ºC. After equilibrium was established, it was found that 28% of the NOCl had dissociated according to the equation 2NOCl(g) 2NO(g) + Cl2(g).

Calculate the equilibrium constant, Kc, for the reaction.
A.
0.021
B.
0.039
C.
0.169
D.
26
E.
47


9.
At 400ºC, Kc = 64 for the equilibrium H2(g) + I2(g) 2HI(g). If 3.00 mol H2 and 3.00 mol I2 are introduced into an empty 4.0 L vessel, find the equilibrium concentration of HI at 400ºC.
A.
0.15 M
B.
1.2 M
C.
2.4 M
D.
4.8 M
E.
5.8 M


10.
For the following reaction at equilibrium, which one of the changes below would cause the equilibrium to shift to the left?

    2NOBr(g) 2NO(g) + Br2(g),    ΔHºrxn = 30 kJ/mol
A.
Increase the container volume.
B.
Remove some NO.
C.
Remove some Br2 .
D.
Add more NOBr.
E.
Decrease the temperature.


11.
Sodium carbonate, Na2CO3(s), can be prepared by heating sodium bicarbonate, NaHCO3(s).

2NaHCO3(s) Na2CO3(s) + CO2(g) + H2O(g)      Kp = 0.23 at 100ºC

If a sample of NaHCO3 is placed in an evacuated flask and allowed to achieve equilibrium at 100ºC, what will the total gas pressure be?
A.
0.46 atm
B.
0.96 atm
C.
0.23 atm
D.
0.48 atm
E.
0.11 atm


12.
What is the pH of a 0.001 M Ca(OH)2 solution?
A.
3.0
B.
11.0
C.
2.7
D.
17.0
E.
11.3


13.
For hydrosulfuric acid (H2S) Ka1 = 5.7 × 10–8 and Ka2 = 1 × 10–19.
Determine the sulfide ion (S 2-) concentration in a 0.10 M hydrosulfuric acid solution.
A.
0.10 M
B.
7.5 × 10–5 M
C.
5.7 × 10–9 M
D.
1 × 10–19 M
E.
1 × 10–20 M


14.
Calculate the pH of a 0.021 M NaCN solution. [Ka(HCN) = 4.9 × 10–10]
A.
1.68
B.
3.18
C.
5.49
D.
7.00
E.
10.82


15.
Given

HOAc
Ka = 1.8 × 10–5
H2CO3
Ka1 = 4.3 × 10–7
 
Ka2 = 5.6 × 10–11

which of the following solutions (all are 0.01 M) has the highest pH?
A.
HOAc
B.
NaOAc
C.
Na2CO3
D.
H2CO3
E.
NaHCO3


16.
Identify the conjugate base of HCO3– in the following reaction:
    CO32– + HSO4– HCO3– + SO42–
A.
HSO4–
B.
CO32–
C.
OH–
D.
H3O+
E.
SO42–


17.
Calculate the pH of a solution that is 0.25 M in benzoic acid (C6H5CO2H) and 0.15 M in sodium benzoate (C6H5COONa). [Ka = 6.5 × 10–5 for benzoic acid]
A.
3.97
B.
4.83
C.
4.19
D.
3.40
E.
4.41


18.
Over which pH range may an indicator with a Ka of 3.16 x 10 - 8 be used?
A.
pH 2.5 – pH 4.5
B.
pH 4.5 – pH 6.5
C.
pH 6.5 – pH 8.5
D.
pH 8.5 – pH 10.5
E.
pH 10.5 – pH 12.5


19.
What is the pH at the equivalence point in the titration of 100 mL of 0.10 M HCN (Ka = 4.9 × 10–10) with 0.10 M NaOH?
A.
3.00
B.
6.00
C.
7.00
D.
11.00
E.
12.00


20.
A 50.00 mL sample of 0.10 M HNO2 (nitrous acid, Ka = 4.5 × 10–4) is titrated with a 0.10 M KOH solution. After 25.00 mL of the KOH solution is added, the pH in the titration flask will be
A.
2.17
B.
3.35
C.
2.41
D.
1.48
E.
7.00


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