1
Seat No.: _____ Enrolment No.______
GUJARAT TECHNOLOGICAL UNIVERSITY
B.E. Sem.-III (Biotechnology) Examination December 2009
Subject code: 130405 Subject %ame: Thermodynamics
Date: 29 /12/ 2009 Time: 11.00 am – 1.30 pm
Total Marks: 70
Instructions:
1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
4. %otations used have their conventional meanings.
Q.1
(a)
Explain PVT behavior of pure substances with the help of PT and PV
diagrams.
07
(b)
Derive a mathematical expression of the first law of thermodynamics for a
steady state flow process between a single entrance and a single exit.
07
Q.2
(a)
Handbook values for the latent heat of vaporization in J/g are given in the
table for the pure liquids at T
n
, the normal boiling point.
Component
υ
∆
l
H
at
T
n
(J/g) T
n
(K) P
c
(bar) T
c
(K)
Benzene 393.9 353.2 48.98 562.2
Toluene 363.2 383.8 41.06 591.8
For these substances, calculate the value of the latent heat at T
n
by Riedel
equation and find out the percentage difference from those listed in the
table.
07
(b)
A particular quantity of an ideal gas C
v
= (5/2) R undergoes the following
mechanically reversible steps that together form a cycle. The gas, initially
at 1 bar and 300 K, is compressed isothermally to 3 bar. It is then heated at
constant P to a temperature of 900 K. Finally; it is cooled at constant
volume to its initial state with the extraction of 1,300 J as heat. Determine
Q and W for each step of the cycle and for the complete cycle.
07
OR
(b)
Nitrogen gas is confined in a cylinder and the pressure of the gas is
maintained by a weight placed on the piston. The mass of the piston and
the weight together is 100 kg. The acceleration due to gravity is 9.81 m/s
2
and the atmospheric pressure is 1.01325 bar. Assume frictionless piston.
Determine:
i) The force exerted by the atmosphere, the piston and the weight on the
gas if the piston is 200 mm in diameter.
ii) The pressure on the gas.
iii) If the gas is allowed to expand pushing up the piston and the weight by
500 mm, what is the work done by the gas in kJ?
07
Q.3
(a) If the heat capacity of a substance is correctly represented by an equation of
the form, Cp = A + BT + CT
2
, show that the error resulting when <Cp>
H
is
assumed equal to Cp evaluated at the arithmetic mean of the initial and
final temperatures is C(T
2
– T
1
)
2
/ 12.
05
(b)
A special manometer fluid has a specific gravity of 3.65 and is used to
measure a pressure of 1.25 bar at a location where the barometric pressure
is 760 mm Hg. What height will the manometer fluid register?
05
