West Bengal State University: B.Sc./Part-I/Hons./CEMA-II/2017

B.Sc./Part-I/Hons.
/CEMA-II/2017
WEST BENGAL STATE UNIVERSITY

B.Sc. Honours PART-I Examinations, 2017
CHEMISTRY-HONOURS
PAPER-CEMA-II
Time Allotted: 2 Hours Full Marks: 50
The figures in the margin indicate full marks.

Candidates should answer in their own words and adhere to the word limit as practicable.
All symbols are of usual significance.
CEMAT-12-PA and CEMAT-12-PB

CEMAT-12-PA
Answer any two questions taking one from each Unit.
Unit-I
1. (a) What should be the value of average kinetic energy at temperature T for 1 3+2+1
mol of an ideal gas restricted to move in 2 dimensions, and why? Obtain
from this result an estimate of the mean square speed. How does it compare
with the square of the mean speed?
(b) Two gases of molar masses M1 and M2 show identical Maxwell’s speed 2
distribution curves at temperatures T1 and T2, respectively. Explain when
such an observation will be valid.
(c) Find the values of   CP CV for monatomic and diatomic gases, assuming 3
ideality.
(d) Suppose that at some initial time all the molecules in a container have the 2
same transitional energy, 2.0 1021J . As time passes, the motion becomes
chaotic and the energies finally are distributed in a Maxwellian way.
Calculate the final temperature of the system.
Turn Over
1024 1
B.Sc./Part-I/Hons./CEMA-II/2017
2. (a) On what factors does the frequency of binary collisions per unit volume 2+2
depend? How does it rise with temperature? Explain.
(b) Define mean free path of a gas molecule. Derive an expression for the mean 1+2+1
free path of a gas molecule in terms of its diameter. How does it depend on
temperature?
(c) Calculate the number of wall collisions per second per square centimeter of 3
O2 molecules at 25°C and 1 atm.
(d) Explain the dependence of viscosity of gases on temperature, assuming no 2
intermolecular attraction.
Unit-II
3. (a) Starting from definition, find an expression for the Boyle temperature of a 4
van der Waals gas.
(b) If the variation of compressibility factor Z with pressure P for the gas CO2 at 1+2+1+2
some low temperature T is fitted by a quadratic expression of the form
Z  a0  a1P  a2 P 2 ,
remark on (i) the value of a0, (ii) the signs of a1 and a2, (iii) the minimum
value of Z, and (iv) the dependence of a1 on T as Boyle temperature is
approached.
(c) A steel ball of radius 2 mm is found to fall with a terminal velocity 1 cm s–1 2
in a liquid of density 1.8 g cm–3 and viscosity 54 poise. Find out the density
of steel.
4. (a) What is a critical point? Justify whether an equation of state of the form 3
P(V  nb)  nRT would show any such point.
(b) Indicate with the help of a sketch, the angle of contact () of a liquid on a 3
solid surface. Obtain an expression for  indicating the factors on which the
value of  depends. What does wetting of a solid surface by a liquid imply?
(c) The critical temperature and pressure for O2, a van der Waals gas, are 154 K 2+1
and 50.3 atm respectively.
Calculate (i) the diameter of O2 molecules and
(ii) the Boyle temperature of the gas.
(d) What is Reynold number? State the differences between streamline flow and 3
turbulent flow.
1024
2
CEMAT 12-PB
Answer any two questions taking one from each Unit
Unit-I
5. (a) 2 mol of an ideal gas (  7 5) is adiabatically expanded to reduce its 3
temperature from 300 K to 200 K. Calculate the work done and U .
(b) Show that the work done in a reversible process is numerically greater than 3
that in an irreversible one.
(c) Draw a T-S diagram for a Carnot cycle indicating isothermal and adiabatic 3+1
steps. Explain the significance of the enclosed area.
(d) Establish that entropy change is related to unavailable work. 3
6. (a) Show that in a reversible adiabatic expansion of an ideal gas, the increase in 3
entropy due to expansion of the gas is exactly compensated by the decrease
in entropy due to cooling of the gas.
 C  2
(b) Show that for an ideal gas  p   0 .
 P T
S  C  3
(c) Show that 
Cp
  where dS   p .dT  V . dp . The terms have
 V  p , n TV T 
their usual significances, and  is coefficient of thermal expansion.
(d) How would you determine enthalpy of a reaction from bond energy? 2
(e) One mole of an ideal monoatomic gas at 300 K and 1 atm is expanded 3
adiabatically against vacuum to double its original volume. Calculate  U ,
 H and  S of the process.
Turn Over
1024 3
Unit-II
7. (a) Consider the following sequential reaction scheme: 3
A 
k1
I 
k2
P.
Assuming that only A is present initially, derive an expression for the time
dependence of P  using steady state approximation.
(b) Consider two reactions I and II. The frequency factor of I is 100 times that 3
of II and the activation energy of I is 4.605 k cal mol 1 higher than that of II.
Show that the two rate constants are nearly equal at 227°C.
(Given R = 2 cal K 1 mol 1 ).
(c) What value will the Arrhenius rate constant take when T   ? What is the 1+2
significance of this quantity?
(d) A reaction S  P is zero order with respect to the substrate S. Show 2+1
graphically how the concentration of S depends on time t. Evaluate also the
half life  1 2 of S.
8. (a) Establish how the frequency factor of a bimolecular reaction is related to 3

 S# .
(b) Explain how the rate of an enzyme-catalyzed reaction depends on the pH of 3
the medium and why.
(c) Show that for a first-order reaction, the time required for 99.9% completion 3
of the reaction is almost 10 times the time for 50.0% completion.
(d) If the activation energy for the gaseous reaction H2  I2  2HI is 167 kJ 3
and the  H for the reaction is – 8.2 kJ, what is activation energy for the
decomposition of HI?
1024
4

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B.Sc./Part-I/Hons.

WEST BENGAL STATE UNIVERSITY

The figures in the margin indicate full marks.

CEMAT-12-PA and CEMAT-12-PB

Answer any two questions taking one from each Unit

8. (a) Establish how the frequency factor of a bimolecular reaction is related to 3

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