12 February 2020
Chapter 8 – Reaction Kinetic Chapter 9- Thermochemistry Chapter 10- Electrochemistry
CHAPTER 8 : REACTION KINETIC 1.
(a)
Compound B has a constant half-life and its half-life does not depend on the concentration. (i) What is the order of this reaction? (ii)
Sketch the graph to display the variation rate of reaction versus time for this reaction.
(iii)
If compound B loses 95% of its activity in 110 minutes, determine its half-life.
(8 marks) (b)
In a decomposition of C → 2D, the rate constant at 298 K is 2.95x10-2 s-1 when the activation energy is 70.8 kJmol-1. (i)
Determine the frequency factor, A for this reaction using Arrhenius equation.
(ii)
What happened to parameter A if temperature increases?
(iii)
Calculate new temperature in Kelvin if rate constant is decrease to 6.61x10-5 s-1.
(iv)
If parameter A is called the frequency factor, what factor is interpreted as the fraction of molecules having at least the minimum energy required for reaction? (6 marks)
2.
(a)
Oxidation reaction of oxalate ions by manganate (VII) ions produces the manganese (II) ion occur in acidic solution. In an experiment of this reaction, the following results in table 1 were obtained. 2MnO4- + 5C2O42- + 16H+ → 2Mn2+ + 10CO2 + 8H2O Experiment 1 2 3 4 (i) (ii) (iii) (iv)
Initial concentration (mol dm-3) MnO4C2O42H+ 0.1 0.1 0.1 0.3 0.1 0.1 0.3 0.1 0.2 0.3 0.2 0.2 Table 1
Initial rate of formation of Mn2+ (Ms-1) x 3x 6x 6x
Determine the order of the reaction with respect to each reactant. Write the rate equation for the above reaction. What is the value of the rate constant? What is the rate formation of H2O in experiment 1? (8 marks)
(b)
A free radical substitution reaction at 300 K is given as follows: C2 + B ∙ → BC + C ∙ The activation energy for the forward and reverse reaction are 127 kJ mol-1 and 18 kJ mol-1 respectively. (i) (ii) (iii)
Draw and label the energy profile diagram. Determine the heat change for the forward reaction. Calculate the frequency factor, A for forward reaction if the rate constant is 9.88x10-11 s-1. (6 marks)
CHAPTER 9 : THERMOCHEMISTRY 3.
(a)
A piece of chocolate (C7H8N4O2) weighing 4.02 g was burned in a bomb calorimeter and increase a temperature by 4.46oC. In the same calorimeter, combustion of 0.25 g sample of benzoic acid, C6H5COOH increase a temperature by 2.92oC. The enthalpy of combustion of benzoic acid is -3227 kJmol-1. (i)
Determine heat capacity of the calorimeter.
(ii)
Calculate the enthalpy of combustion of chocolate. (7 marks)
(b)
Using the data in table 2 below, construct a Born-Haber cycle for the formation of X2O3. Calculate the lattice energy for X2O3. Enthalpy Enthalpy Formation of X2O3
∆Ho (kJmol-1) -1675.7
Enthalpy Atomisation of X
+330.0
Enthalpy Atomisation of Oxygen
+249.0
First Ionisation Energy of X
+578.0
Second Ionisation Energy of X
+1820.0
Third Ionisation Energy of X
+2750.0
First Electron Affinity of Oxygen
-142.0
Second Electron Affinity of Oxygen
+798.0
Table 2 (7 marks)
4.
(a)
100 ml of 2.0 M HCl and 100 ml KOH solution, both at initial temperature of 30oC are mixed in a calorimeter. The maximum temperature of the solution is 41oC. Calculate the enthalpy of neutralization for the reaction. Calculate the enthalpy of neutralization for the reaction. (5 marks)
(b)
The industrial process for the production of sulphuric acid has three steps. S (s) + O2 (g) → SO2 (g) 2SO3 (g) → O2 (g) + 2SO2 (g) SO3 (g) + H2O (l) → H2SO4 (l)
∆H = -296.83 kJ ∆H = -198.20 kJ ∆H = -227.72 kJ
Using the above data, calculate the enthalpy of the reaction, 2S (s) + 3O2 (g) + 2H2O (l) → 2H2SO4 (l) (3 marks) (c)
The thermochemical processes involved in the formation of calcium fluoride, CaF2 are given in Table 3 . Construct a Born-Haber cycle for CaF2 in the solid state by using the data below. Calculate the lattice energy of CaF2. Reactions First ionization energy of Ca
Enthalpy, ∆Ho (kJmol-1) +590
Second ionization energy of Ca
+1150
Standard enthalpy atomization of Ca
+178
Bond energy of F-F bond
+158
Electron affinity of F
-328
Standard enthalpy of formation of CaF2
-1220
Table 3 (6 marks)
CHAPTER 10 : ELECTROCHEMISTRY
5.
(a)
A galvanic cell is made up of one half-cell that consists a zinc electrode immersed in 0.1 M of Zn2+ solution and another half-cell that consists a nickel electrode immersed in 0.001 M of Ni2+ solution. Both half-cells are connected by a salt bridge at 25oC. [Eo Zn2+/Zn =-0.76 V, Eo Ni2+/Ni =-0.25 V]
(i)
Write the cell notation of the galvanic cell.
(iii)
Calculate the cell potential of the galvanic cell. (5 marks)
(b)
A current of 7.50 A is passed through a solution of aluminium (III) chloride, AlCl3 for an hour. Calculate the mass of aluminium deposited at the cathode. (6 marks)
6.
(a)
The cell potential for the following galvanic cell at 25oC is 2.20 V. (Eo Zn2+/Zn= -0.76 V ; Eo Cl2/Cl- = +1.36 V) Zn (s) |Zn2+ (aq, 0.05 M) || Cl- (aq, 0.1 M) | Cl2 (g, y atm) | Pt (s) (i)
Write an overall cell reaction equation.
(ii)
Calculate the pressure of chlorine gas used (value of y) in the cell. (4 marks)
(b)
In a laboratory, a student carries out an electrolysis experiment of CuSO4 using copper electrodes to determine the Faraday constant. After 10 minutes experiment, the data recorded as in table 4. Initial mass of Cu electrode
7.0003 g
Final mass of Cu electrode
7.0310 g
Ammeter reading
0.15 A Table 4
What is the experimental value for the Faraday constant? (6 marks)