CORK INSTITUTE OF TECHNOLOGY
INSTITIÚID TEICNEOLAÍOCHTA CHORCAÍ
Semester 2 Examinations 2009/10
Module Title:
Physical Chemistry 1
Module Code:
CHEM6004
School :
Science
Programme Title:
Bachelor of Science in Analytical & Pharmaceutical Chemistry – Stage 1
BSc in Analytical Chemistry with Quality Assurance – Stage 1
Programme Code:
SCHEM_7_Y1
SCHQA_8_Y1
External Examiner(s):
Internal Examiner(s):
Dr. G. Keaveney
Dr. M. Sheahan
Instructions: Answer any FOUR questions
Duration:
2 Hours
Sitting:
Summer 2010
Requirements for this examination:
Periodic Table
Note to Candidates: Please check the Programme Title and the Module Title to ensure that you have
received the correct examination paper.
If in doubt please contact an Invigilator.
Q1.
(a) The thermal decomposition of lead nitrate, Pb(NO3)2
may be expressed by the
following equation
2Pb(NO3)2(s)
(i)
∆
2PbO(s) + 4NO2(g) + O2(g)
Give an expression which shows how the rate of decomposition of the lead nitrate
is related to the rate of production of lead oxide (PbO)
If nitrogen dioxide is forming at a rate of 1.34 x 10− 4 Ms−1, at what rate is oxygen
(ii)
being produced and lead nitrate decomposing?
(6 marks)
(b) Aluminium reduces iron oxide (Fe2O3) to elemental iron and aluminium oxide
(Al2O3) according to the equation below. The reaction is highly exothermic (852kJ)
Fe2O3(s) + 2Al(s)
2Fe(s) + Al2O3(s)
What heat change occurs when
(i)
one mole of aluminum is used
(ii)
0.1 moles of elemental iron reacts with aluminum oxide
(4 marks)
(c) The following reaction has an equilibrium constant (Kc) of 3.59 at 900°C.
CH4(g) + 2H2S(g)
CS2(g) + 4H2(g)
(i) Comment on the position of the equilibrium in this reaction.
(3 marks)
(ii) Calculate the equilibrium constant if 3 moles of methane were reacted with the
appropriate amount of hydrogen sulfide (H2S)
(iii)What is the value of the equilibrium constant for the reverse reaction
(3 marks)
(3 marks)
(d) Write a balanced equation showing the dissociation of each of the following acids in
water: C6H5COOH, HIO3, HPO42– and HS–. Identify the conjugate base of each acid
(6 marks)
Q2.
(a) What do you understand by the following terms in thermodynamics: standard state,
enthalpy, entropy and work?
(b)
(8 marks)
(i) Use the data in the table provided to calculate the standard enthalpy change for
the combustion of ammonia.
4NH3(g) + 5O2(g)
(3 marks)
4NO(g) + 6H2O(g)
(ii) Would you say the reaction is spontaneous? Give reason(s) for your answer
(3 marks)
(iii) State Hess’s Law. What method uses the principles of Hess’s Law to
determine the enthalpy change in the reaction?
(5 marks)
(c) Nitrogen dioxide (NO2) may be generated according to the equation
N2(g) + 2O2(g)
2NO2(g)
Consult the standard molar enthalpy table to determine if the reaction is endothermic
or exothermic? Hence calculate the enthalpy change (in kJ) when the two moles of
NO2 are produced. Is work done on or by the system?
(6 marks)
Q3.
− Ea/RT
(a) What does the term ‘A’ represent in the equation k = A e
?
(2 marks)
(b) What do you understand by the activation energy of a reaction? Use the Arrhenius
equation to derive two expressions which may be used to determine the activation
energy of a reaction
(7 marks)
(c) The tabulated data has been determined for the hydrolysis of ethyl iodide (C2H5I):
C2H5I (aq) + OH−(aq)
C2H5OH(aq) + I− (aq)
k (M-1s-1) 5.03 x 10-5 3.68 x 10-4 6.71 x 10-3 0.119
T (°C)
15.83
32.02
59.75
90.61
(i) Construct the appropriate plot and determine the activation energy (Ea) for this
reaction. Express your answer in kJ. (R = 8.314 J mol-1 K-1)
(12 marks)
(ii) Calculate the value of the rate constant if the temperature is increased to 120°C
(4 marks)
Q4.
(a) The oxidation of the sulfur dioxide (SO2) to sulfur trioxide (SO3) is a slow exothermic
reaction under normal conditions of temperature and pressure. Since this is the first
step in the industrial synthesis of sulfuric acid, it is necessary that the reaction is
efficient (i.e. good yield in reasonable time frame). Discuss in detail the reaction
conditions which you think would maximize the output from this reaction.
(12 marks)
(b) In a reaction 0.455 mole SO2, 0.183 moles O2 and 0.568 moles SO3 are introduced
into a 1.90L vessel at 1000K. Calculate the molarity of each species in the reaction
vessel
(2 marks)
2SO2(g) + O2(g)
2SO3(g)
Perform and show the appropriate calculations to establish if this mixture is at
equilibrium? If not, in which direction will a net change occur? Kc for the oxidation of
SO2 at 1000K is 2.8 x 102
(5 marks)
(c) Write solubility equilibrium equations corresponding to the following Ksp
expressions:
Ksp = [Fe3+][OH−]3
Ksp = [Pb2+][Br −]2
Ksp = [Ag+]2[SO42−]
(6 marks)
Q5.
(a) Derive the Henderson Hasselbalch equation. Use this equation to calculate the pH of
a buffer solution prepared by mixing equal volumes of 0.5M acetic acid (CH3COOH)
and 0.5M sodium acetate (CH3COONa). Ka for acetic acid is 1.8 x 10-5 at 25°C
(10 marks)
(b) Four solutions A, B, C and D were prepared by transferring the volumes indicated in
the table to a series of beakers.
A
B
C
D
0.5M CH3COOH 50 cm3 6 cm3 4 cm3 0 cm3
0.5M CH3COONa 10 cm3 54 cm3 56cm3 24 cm3
What is the effect on the pH when a small volume (ca. 1cm3) of HCl is added to each
solution? Support your answers with the relevant reaction equations.
(5 marks)
(c) What is the common-ion effect in ionic equilibria? Calculate the pH of a 0.1M
solution of nitrous acid (HNO2, Ka = 4 x 10-4) and explain the effect on the pH of this
solution if the salt sodium nitrate (NaNO2) is added to it.
(d) Why have solutions of sodium acetate (CH3COONa) an alkaline pH?
(6 marks)
(4 marks)
Q6.
(a) Construct a Galvanic cell for the redox reaction between chromium (Cr) and silver
(Ag). (note: Cr is higher in the activity series of metals than Ag). Label the anode
and the cathode, give the sign of each electrode, and indicate the direction of electron
flow.
(10 marks)
(b) Write an equation for both half-cell reactions and clearly identify the oxidizing and
reducing agents respectively.
(6 marks)
(c) Comment on the function of a salt bridge in galvanic cells. Give examples of two
types of salt bridge.
(5 marks)
(d) What weight of sodium metal is produced when a current of 30A is passed through
molten NaCl for a 2.00hr period?
(4 marks)