Fall 2010
Chem 1B, Test Review #2
1.
The following kinetics data were obtained for the reaction:
2NO(g) + Cl2(g)  2NOCl(g)
Expt.#
[NO]0 (mol/L) [Cl2]0 (mol/L) Initial Rate, (mol/L.s)___
1
0.20
0.10
0.63
2
0.20
0.30
5.70
3
0.80
0.10
2.53
4
0.40
0.20
?

(a) Determine the rate law for this reaction and calculate the value of the rate constant, k.
(b) What is the initial rate when the concentrations are [NO]0 = 0.40 M and [Cl2]0 = 0.20 M ?
(Answer: (a) k = 320 L2.mol-2.s-1; (b) Rate = 5.1 mol/L.s)
2.
The re-arrangement of methyl isonitrile to methyl cyanide: CH3NC  CH3CN, follows
first order kinetics with rate constant, k = 3.3 x 10-3 s-1 at 250oC.
(a) What is the half-life for this reaction at 250oC?
(b) Start with 0.100 M methyl isonitrile (CH3NC), what would be the concentration of CH3NC after
10.0 minutes of reaction has elapsed? (c) How long does it take for 90.0% of the original amount of
CH3NC to undergo re-arrangement? (Answer: (a) 210 s; (b) 0.014 M; (c) 698 s = 11.6 minutes)
3.
The concentration of a reactant that follows a first order rate law decreases from 0.15 mol/L to 0.025
mol/L in 96 seconds. What are the half-life and the rate constant for this reaction?
(Answer: half-life = 160 s; k = 4.2 x 10-3 s-1)
4.
The following mechanism has been proposed for the reaction between methane and chlorine gas:
Step 1: Cl2 ⇄ 2 Cl
Step 2: CH4 + Cl.  HCl + .CH3
Step 3: Cl. + .CH3  CH3Cl
(fast, equilibrium)
(slow, rate-determining)
(very fast)
(a) Write the net equation for the overall reaction.
(b) What is the molecularity of the rate-determining step?
(c) Identify all reaction intermediates.
(d) Derive the rate law for the reaction.
5.
The reaction: N2O4(g)  2 NO2(g) has Ho = 58.0 kJ.
The reaction follows first order rate law with rate constants, k = 4.5 x 10-2 s-1 and 1.0 x 10-1 s-1 at 315
K and 324 K, respectively. (a) Calculate the activation energy, Ea, for the decomposition of N2O4.
(b) What is the activation energy for the reverse reaction? (c) Assuming a constant activation energy,
determine the rate constant (k) at 25oC and the rate for the decomposition of N2O4 at 25oC when
[N2O4] = 0.15 M. (Answer: (a) Ea = 75.3 kJ/mol; (b) Ear = 17.3 kJ; (c) k = 8.7 s-1)
1
Fall 2010
Chem 1B, Test Review #2
6.
7.
Under what temperature conditions (high or low) is each of the following reactions spontaneous or
not spontaneous?
(a) H2C=CH2(g) + H2(g)  CH3CH3(g);
Ho = -137 kJ
(b) CH4(g) + NH3(g)  HCN(g) + 3 H2(g);
Ho = +252 kJ
(c) 2 N2(g) + O2(g)  2 N2O(g);
Ho = +164 kJ
(d) C2H5OH(l) + 3 O2(g)  2 CO2(g) + 3 H2O(g);
Ho = -1236 kJ
Given the following Thermodynamics data:
CO2(g)
H2O(l)
NH3(g)
CO(NH2)2(s)
Hof (kJ/mol):
-393.5
-285.85
-45.9
-333.2
So (J/K.mol):
214
193
105
70
(a) Calculate Ho, So, and Go for the following reaction at 25oC:
CO2(g) + 2NH3(g)  CO(NH2)2(s) + H2O(l) at 25oC.
(b) What is the equilibrium constant, Kp, for this reaction at 25oC? (c) At what temperature this
reaction would have Go = 0.
(Answer: Ho = -133.8 kJ; So = -425 J/K; Go = -7.15 kJ; (b) Kp = 17.9; (c) T = 315 K)
8.
The reaction: CO(g) + 2 H2(g)  CH3OH(g) has Ho = -90.5 kJ and So = -220 J/K. Determine
whether the reaction is spontaneous at 500 K: (a) under standard pressure condition; (b) under the
following conditions: PCO = 30.0 atm; PH2 = 60.0 atm; PCH3OH = 10.0 atm. (R = 8.314 J/mol.K)
9.
Given the following reactions:
2NO2(g)  2NO(g) + O2(g);
2SO2(g) + O2(g)  2SO3(g);
Go = +71.2 kJ
Go = -141.6 kJ
What is Go and Kp for the following reaction at 25oC? Indicate if the forward reaction is spontaneous
or not spontaneous.
SO2(g) + NO2(g)  SO3(g) + NO(g);
(Answer: Go = -70.4 kJ; Kp = 2.19 x 1012)
10.
(a) Given that Hof[C2H5OH(l)] = -277.6 kJ/mol and Hof[C2H5OH(g)] = -235.1 kJ/mol, calculate the
enthalpy of vaporization of ethanol at its normal boiling point of 78oC. (b) What is Sovap for ethanol?
(c) If So[C2H5OH(l)] = 161 J/K.mol, what is So[C2H5OH(g)]? (d) What pressure must be applied to raise
the boiling point of ethanol to 100oC? (R = 8.314 J/mol.K)
(Answer: (a) Hovap = 42.5 kJ; (b) Sovap = 121 J/K; (c) So[C2H5OH(g)] = 282 J/K.mol; (d) 2.33 atm)
2
Fall 2010
Chem 1B, Test Review #2
11.
Consider the following standard reduction (half-cell) potentials:
Al3+(aq) + 3e-  Al(s);
Eo = -1.66 V
Cu2+(aq) + 2e-  Cu(s);
Eo = +0.34 V
(a) Write the cell notation of a voltaic cell that uses the above half-cells and write net ionic equation
for the cell reaction. (b) Sketch the cell diagram, label the anode and cathode half-cells, and indicate
the direction of electron flow in the external circuit and the flow of ions in solutions. (c) Calculate
the standard cell potential (Eocell) and Go for the overall reaction at 25 oC. (d) What is the cell
potential at 25oC if the electrolyte concentrations are: [Al3+] = 0.0010 M and [Cu2+] = 1.0 M?
(e) How much energy (in kJ) can be derived from the oxidation of 1.54 g of aluminum at an average
cell potential of 2.00 V? (Answer: (c) Eocell = 2.00 V; (d) 2.06 V; (e) 33.0 kJ)
12.
In an electrolysis of CuSO4(aq) solution, a constant current of 25.0 A passes through the solution for
30.0 minutes. (a) How many grams of copper are formed and in which electrode? (b) What other
product is formed and on which electrode? (c) If the electrolytic cells operate at a constant voltage of
3.0 V, how much energy (in kJ) is consumed? (Answer: (a) 14.8 g Cu; (c) 135 kJ)
13.
Aluminum is produced by electrolysis of molten Al2O3-Na3AlF6 mixture using a series of electrolytic
cells that operates at a total voltage of 4.5 V and a constant current of 1.5 x 104 A? How many grams
of aluminum can be produced using the above amperage for 1.00 hour? How much energy (in kWhr)
is consumed during the electrolysis? (Answer: 5.0 kg; 68 kWh)
14.
(a) Write balanced equations for the spontaneous reactions in each of the following batteries:
(i) car battery;
(ii) alkaline dry cell;
(iii) “acidic” dry cell.
(b) How many grams of lead are reacted (oxidized) to produce a constant current of 650 A for 5.0
seconds? (c) How much energy (in kJ) is produced if the average battery potential is 12 V?
(Answer: (b) 3.5 g Pb; (c) 39 kJ)
15.
Explain an anodic protection and a cathode protection in corrosion prevention. Give examples and
explain how each protection method works.
3