Redox & Electrochemistry
Thermochemistry
Organic Chemistry
Chemical Equilibrium
Acid-Base Equilibrium
100
In the following reaction,

2 MnSO4 + 5 PbO2 + 3 H2SO4 --> 2 HMnO4 + 5 PbSO4 + 2 H2O

Which is the substance is the oxidizing agent?

PbO2
100
The heat of condensation of water at 373 K is -40.7 kJ/mol.

When 9.00 g of water vaporizes at 373 K, how much heat is needed to boil the water?
∆Hvap = -∆Hcondensation = 40.7 kJ/mol

9.00 g H2O x 1 mol/18.02g x 40.7 kJ/mol = 20.3 kJ
100
What is the IUPAC name for the following condensed structural formula?

(CH3)2CHCHBrCH2CH(C2H5)CH=CH2
5-bromo-3-ethyl-6-methyl-1-heptene
100
Consider the following equilibrium reaction:

S2Cl2(l) + CCl4(l) + 84.3 kJ ⇌ CS2(g) + 3 Cl2(g)

If temperature of the reaction container is decreased, how will the Kc value of the reaction effected? Explain your answer.

Kc value will decrease as decrease temperature because equilibrium shift reverse to replenish lost of heat so system favors reactant.
100
Calculate the pH of a 0.0065 M Ca(OH)2 solution.

[OH-] = 0.013 M
pOH = -log[OH-] = 1.886
pH = 14 - pOH = 12.11 (2 sf)
200
Balance the following half reaction in acidic solution and state whether it is a reduction or oxidation reaction.

V(s) --> HV2O73-(aq)
7 H2O + 2 V(s) --> HV2O73-(aq) + 13 H+(aq) + 10e-

oxidation - loses electron
200
The following reaction,

2 A + B --> C + 2 D + 250 kJ has an activation energy of 135 kJ.

Sketch the energy diagram of the forward reaction. Label the enthalpy change and Ea on the diagram.

a) If a catalyst is added, explain how it will affect the rate of reaction. Sketch the energy diagram with the presence of a catalyst on the graph.

b) For the reverse reaction, what will be the values for the enthalpy change and the activation energy?
Answer is on the board.
200
What type of reaction is being represented by the reaction of hex-2,4-diene with bromine solution?

Draw the structural formulas for the reaction and give the name of the compound(s) formed in the reaction.
Addition reaction

See blackboard for the answer. 2,3,4,5-tetrabromohexane
200
The oxidation of carbon monoxide proceeds as follows:

2 CO(g) + O2(g) ⇌ 2 CO2(g) + 559 kJ

Use Le Chatelier's Principle to predict and explain the effects of decreasing:

a) the temperature

b) the pressure

To get full marks your explanation must be clearly demonstrate your understanding of the Le Chatelier's principle.

a) decreasing temperature - heat is being remove from system hence equilibrium will shift forward to produce heat.

b) decreasing pressure - system needs to increase pressure therefore equilibrium shift reverse (shift from less moles of gases to more moles of gases)
200
In the titration of a strong acid with strong base, what would you predict the pH of the solution at the equivalence point? Sketch a pH titration curve (pH verse volume of base added) to support your answer.

Which of the following indicators would be the best choice for detecting the equivalence point of the titration?

Bromothymol green, pKa = 4.70
Cresol red, pKa = 7.20
Phenolphthalein, pKa = 9.15

Strong acid and strong base titration, the equivalent point of the solution should be close to pH of 7 because the midpoint of the region of rapid pH change (from pH 4 to 10) is equal to 7.

Cresol red would be the most suitable indicator for this titration.
300
Which of the following reactions can occur in an electrolytic cell? Show your work.

1) 2Ag+ + Ni(s) --> Ni2+ + Ag(s)
2) Zn2+ + 2Cl- --> Cl2(g) + Zn(s)
3) 2Fe2+ + Br2(l) --> 2 Fe3+ + 2Br-
Only reaction 2 because cell potential is a negative value
300
Using the Law of Summation and the enthalpies for reactions 1, 2 and 3:

1) A + B --> 2C ∆H1 = 158 kJ
2) C + B --> D ∆H2 = -220 kJ
3) 2A + 2E --> 4D ∆H3 = -74 kJ

Calculate the enthalpy change of the reaction:

3B --> E
∆Hrxn = ∆H1 + 2 ∆H2 + 1/2(-∆H3)

∆Hrxn = 158 kJ + 2(-220 kJ) + 1/2(+74 kJ) = -245 kJ
300
Draw the line structures to represent the following molecules and determine which compounds will form hydrogen bonding between their own molecules.

a) 4-ethyl-6-methyl hept-2-yne

b) 2-chloro-2-methyl pentan-3-ol

c) 4-ethyl-2,5,6-trimethyl oct-1-ene

d) butyl propanoate
See the structure on blackboard.

a) no; b) yes; c) no; d) no
300
NOCl gas decomposes to form NO and Cl2 gases as follow,

2 NOCl(g) ⇌ 2 NO(g) + Cl2

If 0.500 mol of NOCl is placed in a 1.00 L reaction vessel at 700 K, after the system reaches equilibrium, the 0.440 mol of NOCl is found present at equilibrium. Calculate the equilibrium constant Kc for the reaction. (Detective method)
2x = 0.060, x = 0.030

Kc = 5.6 x 10-4

Note that Kc should be rounded to 2 SF because equilbrium concentrations are 2 SFs and solving for Kc involved multiplication and division so you look at the least amount of SF.
So I'm correct... haha :P
300
Calculate the pH of a 0.050 M solution of pyridine, C5H5N, which has a Kb of 1.4 x 10-9. (Ignore x method)

Calculate the equilibrium constant, Ka, of it's conjugate acid?
[OH-] = 8.366 x 10-6
pOH = 5.077
pH = 8.92
Ka = Kw/Kb = 7.1 x 10-6
400
Dimethyl hydrazine, C2H8N2, can be used as a rocket fuel where it undergoes combustion according to the following equation:

C2H8N2(l) + 4 O2(g) --> 2 CO2(g) + 2 H2O(l) + N2(g) + 1694.0 kJ

Use this information together with the heats of formation from the data booklet to calculate the heat of formation for dimethylhydrazine.

-1694.0 = (2 * -393.5) + (4 * -285.8) - x
x = -236.2 kJ/mol
400
How many structural isomers of alcohol with the chemical formula of C5H12O can you come up with? Draw the line structures of the alcohols and name the isomers.
There are 7 possible isomer. See answer on board.
400
For the reaction:

CO2(g) + H2(g) ↔ CO(g) + H2O(g)

The Kc is equal to 1.6 at 1260 K. If 0.15 moles of CO2 and H2 gases are introduced to a 1.25 L flask, what are the concentrations of all four gases when equilbrium is reached? (Perfect square method)
[CO]eq = [H2O]eq = 0.067 M
[CO2]eq = [H2]eq = 0.053 M
400
A 0.10 M solution of ethanoic acid has a pH 2.87. Calculate the acid dissocation constant, Ka, for this acid? (don't look value from the data table)

A buffer solution is prepared by adding sodium ethanoate to the solution of ethanoic acid. Using Le Chatelier's Principle and the equilibrium equation to explain how the buffer solution is able to resist changes in pH when hydrogen and hydroxide ions are added.

Ka = 1.8 x 10-5

HA + H2O <--> A- + H3O+
Added H+ ion reacts with the conjugate base ion in solution hence the system shift reverse to use up the excess H+ ion forming the weak acid resulting in a slight decrease in pH.

Added OH- ion reacts with H3O+ ion forming water hence there is a decrease in concentration of hydronium ion. The system shift forward to produce more H+ ion by dissociation of the weak acid.
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