Thermodynamics (PHYS2140)
BSc, Physics - PHYS
Semester: First Semester
Level: 200
Year: 2017
REPUBLIC OF CAMEROON
Peace —
Work -
Fatherland
The UNIVERSITY OF BAMENDA
P.O. BOX 39 Barnhill
THE UNIVERSITY OF BAMENDA
FACULTY OF SCIENCE DEPARTMENT: PHYSICS
CONTINUOUS ASSESSMENT
COURSE/ CODE/: PHY2140_Thermodynamics
DATE: 05/05/2017 HALL: PBB-08 Time: 07:30 – 10:30am
Instructions: Clarity, concision and Precision will be taken into account
Exercise 1: (18
marks)
1. Represent the behavior of van der Waals gases and real gases in two different
p-V
diagrams. indicate the
region of phases. While comparing, tell what is wrong in van der Waals gases to be improved.
2. Write the van der Waals state equation. Determine the critical point (p
c
, V
c
, T
c
) of van der Waals gases in
terms of constants
a, b
and
R.
where
R = 8.32J I mol.°K
3. Calculate these critical components for water where, a = 0.5536
Pa.m
6
/mo
2
and b = 0.03049x10
-3
m
3
/mol.
4. Calculate the one of ammonia where, a=0.4225
Pa.m
6
/mol
2
and b=0.03707x10
-3
m
3
/mol
5. Which critical point between water and ammonia is above
another?
Exercice 2: (18
marks)
T h e state equ a t i o n o f a r e a l ga s i s w r i t t e n
v = R T ,
w h e r e R = 8 3 2 J /
mo l . ° K
a = 41.4Pa.°K.m
6
/mol . The molar specific heat at constant volume is given
by c
v
=
R
temperature when the
pressure tends to zero.
Write the elementary heat in term of
c
v
and
1
coefficients.
Establish the relations
l = T
and
=
starting by the fact that
dU
and
dS
are full,
Find the expression of C
v
and
l
at temperature
T
and molar volume v of the gas.
Calculate the change ∆C
v
, when the molar volume passes from v
o
to 2v
o
at constant temperature. v
o
= 20
Vmol, T =
20°K.
Exercise 3: (15
marks)
1. Express the elementary change in entropy of an ideal gas in terms of independent variables
T
and
V.
Deduce the change in entropy of one mole when the initial temperature and initial volume are tripled
simultaneously. y = 715 and
R =
8.32 SI.
2. One mixes at the atmospheric pressure a mass M
1
= 10 kg of water at temperature T
1
= 27 °C, with a
mass
M
2
=
1kg of ice at
T
2
=
-10 °C. Determine the equilibrium temperature
T
and the change in entropy of the
system. The specific heat of water is c
2
=g.°C ,
the specific heat of ice c
2
=
2.15J/g.°C
and the latent heat of
fusion of ice at T
o
= 273°K is
L =336.17/g
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Exercise 4: (19
marks)
In relation with a source of heat of temperature T
A
, a monoatomic perfect gas performs a cyclic process. The
cycle is composed of the adiabatic process (A→ B) followed by the isochoric process (B→C) and end by the
isothermal process (C→A). All these transformations are considered as reversible. The initial state variables are p
A
,
V
A
and T
A
. After the adiabatic process, V
B
= 2V
A
1. Represent the cycle in the
p-V
diagram.
2. Express the state variables (p,
V,
T) at B and C in terms of p
A
, V
A
or
T
A
.
3. Find the expressions of heat Q and work W of each process in the cycle in terms of p
A
, V
A
or
T
A
.
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