M-I-061

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 (R_H)	= 2.179 x 10^-18	J/particle
Faraday (F)	= 96485	Coulombs
Specific heat of H₂O	= 4.18	J/(g.^oC)

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

R = k [A]

C.	R = k[A] [B]²

D.	R = k [A] [B]⁴

E.	R = k [A] [B]

A first order reaction of the type

aA → products

has a half life, t_1/2, of 138.6 s. The time needed for the A concentration to drop
20 % from its initial value is:

44.6 s

444 s

111 s

322 s

32.0 s

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.

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 – ⁴M min –¹.

E.	1.24 x 10 –⁴ M min –¹.

The reaction
aA → products

is first order with a rate constant of 1.68 x 10 –² s^–¹ 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?

0.91

0.18

1.0

0.69

0.50

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:

0.35

1.4

0.42

1.7

0.83

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.

For the reaction

2A (g) ⇌ B (g) + C (g)

K_p 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?

3.00 atm

5.67 atm

2.67 atm

2.88 atm

4.41 atm

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?

0.452 M

0.248 M

0.205 M

0.495 M

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) K_c = 5.0 x 10 –³¹

B.	2 H₂ (g) + O₂ (g) ⇌ 2 H₂O (g) K_c = 1.7 x 10 ²⁷

C.	H₂ (g) + Cl₂ (g) ⇌ 2 HCl (g) K_c = 3.2 x 10 ¹⁶

D.	2 HF (g) ⇌ H₂ (g) + F₂ (g) K_c = 1.0 x 10 –¹³

E.	2 NOCl (g) ⇌ 2 NO (g) + Cl₂ (g) K_c = 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, K_b, of the weak base?

A.	9.81 x 10 –⁷

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, K_a, for acetic acid (C₂H₃O₂H) is 3.78 x 10 –⁷?

9.76

4.24

3.51

6.42

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?

3.0 %

9.0 %

3.8 %

1.7 %

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) ; K_a1= 4.3 x 10 –⁷
HCO₃ – (aq) ⇌ H ⁺ (aq) + CO₃ ^2– (aq) ; K_a2= 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 K_b = 1.8 x 10 –⁵.

9.26

10.26

8.96

10.98

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 ⁷calculate 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. K_a 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 (S^2–)
concentration was adjusted to 1.0 x 10 –²⁰ M. Given that:

K_sp (CdS) = 8.0 x 10 –²⁷

K_sp (CuS) = 6.3 x 10 –³⁶
K_sp (FeS) = 6.3 x 10 –¹⁸

which of the sulfides will precipitate?

A.	CdS and CuS.

CuS only.

C.	CuS and FeS.

FeS only.

E.	All three sulfides.

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