Practice Questions for Final Exam

CHM 2045 2006

1. The gas-phase reaction A Æ B has been studied in a closed vessel, and the rate

equation was found to be: rate = -Δ[A]/Δt = k[A]. Which one of the following actions is

least likely to cause a change in the rate of the reaction?

A) lowering the temperature B) adding a catalyst C) using a larger initial amount of A

in the same vessel D) using a bigger vessel, but the same initial amount of A

E) continuously removing B as it is formed.

2. Consider the following mechanism for the oxidation of bromide ions by H2O2:

+ + H2O2 Æ H2O+--OH (rapid)

2O+--OH + Br - Æ HOBr + H2O (fast)

HOBr + H+ + Br - Æ Br2 + H2O (fast)

What is the overall reaction equation for this process?

A) 2HO

B) 2H

+--OH + 2Br - Æ H2O2 + Br2 + 2 H2O

+ + 2Br - + H2O2 Æ Br2 + 2H2O

C) 2H

+ H2O2 + Br - + HOBr Æ H2O+--OH + Br2 + H2O

D) H

2O+--OH + Br - + H+ Æ Br2 + H2O E) none of these

3. If the activation energy of a reaction decreases by 10.0 kJ/mol, from 100 to 90

kJ/mol, what effect will this have on the rate of a reaction at 298 K?

A) rate will increase by a factor of >50 B) rate will decrease by a factor of >50

C) rate will increase by a factor of <50 D) rate will decrease by a factor of < 50

E) rate will not change unless temperature changes

4. Ammonia will react with oxygen with a copper catalyst to form nitrogen and

water. From 164.5oC to 179.0oC, the rate constant increases by a factor of 4.27.

What is the activation energy of the reaction?

A) 24.5 kJ/mol B) 165 kJ/mol C) 242 kJ/mol D) 1630 kJ/mol E) >104 kJ/mol

5. If 75 grams of benzaldehyde (M = 106.1 g/mol) is dissolved in 850 grams of

ethanol(Kf = 1.99oC/m), what is the freezing point of the solution? The freezing

point of pure ethanol is -117.3oC

A) -117.5 B) -118.5 C) -119.0 D) -122.0 E) -125.3

6. Calculate the molality, m, of a solution prepared by dissolving 45.38 g of CdBr2 in

375.0 g of water.

A) 0.03035 m B) 0.01600 m C) 0.1210 m D) 0.4446 m E) none of the above

7. Colligative properties depend on:

A) the chemical properties of the solute

B) the chemical properties of the solvent

C) the masses of the individual ions

D) the molar mass of the solute

E) the number of particles dissolved

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Practice Questions for Final Exam

CHM 2045 2006

The gas-phase reaction A Æ B has been studied in a closed vessel, and the rate equation was found to be: rate = -Δ[A]/Δt = k[A]. Which one of the following actions is least likely to cause a change in the rate of the reaction?

A) lowering the temperature B) adding a catalyst C) using a larger initial amount of A in the same vessel D) using a bigger vessel, but the same initial amount of A E) continuously removing B as it is formed.

Consider the following mechanism for the oxidation of bromide ions by H 2 O 2 :

H+^ + H 2 O 2 Æ H 2 O+--OH (rapid) H 2 O+--OH + Br -^ Æ HOBr + H 2 O (fast) HOBr + H+^ + Br -^ Æ Br 2 + H 2 O (fast) What is the overall reaction equation for this process?

A) 2H O 2 B) 2H

+--OH + 2Br - (^) Æ H 2 O 2 + Br 2 + 2 H 2 O

(^) + 2Br - (^) + H 2 O 2 Æ^ Br 2 + 2H 2 O C) 2H+^ H 2 O 2 + Br -^ + HOBr Æ H 2 O+--OH + Br 2 + H 2 O D) H 2 O+--OH + Br -^ + H+^ Æ Br 2 + H 2 O E) none of these

If the activation energy of a reaction decreases by 10.0 kJ/mol, from 100 to 90 kJ/mol, what effect will this have on the rate of a reaction at 298 K? A) rate will increase by a factor of >50 B) rate will decrease by a factor of > C) rate will increase by a factor of <50 D) rate will decrease by a factor of < 50 E) rate will not change unless temperature changes
Ammonia will react with oxygen with a copper catalyst to form nitrogen and water. From 164.5oC to 179.0oC, the rate constant increases by a factor of 4.27. What is the activation energy of the reaction? A) 24.5 kJ/mol B) 165 kJ/mol C) 242 kJ/mol D) 1630 kJ/mol E) >10^4 kJ/mol
If 75 grams of benzaldehyde (M = 106.1 g/mol) is dissolved in 850 grams of ethanol(Kf = 1.99oC/m), what is the freezing point of the solution? The freezing point of pure ethanol is -117.3oC A) -117.5 B) -118.5 C) -119.0 D) -122.0 E) -125.
Calculate the molality, m , of a solution prepared by dissolving 45.38 g of CdBr 2 in 375.0 g of water. A) 0.03035 m B) 0.01600 m C) 0.1210 m D) 0.4446 m E) none of the above
Colligative properties depend on: A) the chemical properties of the solute B) the chemical properties of the solvent C) the masses of the individual ions D) the molar mass of the solute E) the number of particles dissolved

The aqueous solution with the lowest freezing point of the following group is: A) 0.01 m MgSO 4 B) 0.01 m NaCl C) 0.01 m C 2 H 5 OH D) 0.008 m MgI 2 E) all equal
What is the molar concentration of CO 2 in champagne at 25oC if the partial pressure of CO 2 is 5.5 atm and the Henry’s law constant for CO 2 is 3.2 x 10-2^ M /L atm.

A) 1.1 M B) 0.45 M C) 5.8 M D) 0.20 M E) 0.83 M

The freezing point of benzene is 5.5oC. What is the freezing point of a solution of 5.00 g of naphthalene (C 10 H 8 ) in 444 g of benzene (Kf of benzene = 4.90OC/m) A) 0.43OC B) 5.1oC C) 4.6oC D) 0.86oC E) 4.3oC
An animal cell assumes its normal size (volume) when placed in a solution with a colligative molarity of 0.3M. If the cell is placed in a solution of 0.15M, what happens? A) water leaves the cell, causing contraction B) no water movement takes place C) water enters the cell, causing expansion D) need to know water contents E) need to know cell contents
The reaction: A Æ A*^ is first order. At 100 K, 20% of A reacts in 5.12 min. What is the time for 60% of A to react? A) need a rate constant to know B) 15.4 min C) 48.3 min D) 30.7 min E) 21. min
The reaction : 3 RS 2 Æ 3 R + 6 S shows the following rate data: [RS 2 ] (mol/L) Rate (mol/L.s) 0.150 0.0394 The rate constant (Lmol-1s-1) is: 0.250 0. 0.350 0.214 A) 0.0103 B) 0.263 C) 0. 0.500 0.438 D) 1.17 E) 1.

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Practice Questions for Final Exam

CHM 2045 2006