# Gas

```AL-MC-Gas / p.1
1.
(88-I-12)
D.
For smoke particles undergoing Brownian motion
The average speed of gas molecules
increases.
is air, the motion of the smoke particles is mainly
E.
caused by
The frequency of collision of the gas
molecules with the piston increases.
A.
air convection currents.
4.
B.
the interaction between oxygen and
An ideal gas is at temperature T. If the mass of a
nitrogen molecules.
gas molecule = m, the molar gas constant = R and
C.
collisions between air molecules.
D.
collisions between smoke particles.
E.
collisions between air molecules and
(88-I-17)
N A , then the r.m.s.
speed of the molecules is
smoke particles.
2.
(88-I-14)
An ideal gas is contained in two metal cylinders A
and B connected by a tap, which is initially closed.
The volume and pressure of the gas in the cylinders
are as follows :
pressure / Pa
11 10 3
4  10 3
5 10 5
2 10 5
A
B
volume / m3
When the tap connecting the two cylinders is
5.
A.
3RT / m.
B.
RT /( mN A ) .
C.
3RT /( mN A ).
D.
RTN A / m.
E.
3RTN A / m.
(88-I-18)
opened, what will be the final pressure in the
Which of the following is NOT an assumption in
vessel? Your may assume that the temperature
deriving kinetic theory of gases?
remains constant.
A.
A.
B.
C.
D.
E.
2.4  10 Pa.
3.5  10 5 Pa.
4.2  10 5 Pa.
5.0  10 5 Pa.
6.9  10 5 Pa.
5
The volume of the molecules is
negligible compared with the volume
of the gas.
B.
Attractive forces between the
molecules are negligible.
C.
The duration of a collision is negligible
compared with the time between
3.
(88-I-15)
collisions.
A piston is SLOWLY pushed into a metal cylinder
D.
Collisions with the walls of the
containing an ideal gas. Which of the following
container and with other molecules
statements is INCORRECT?
cause no change in the average kinetic
energy of molecules.
A.
The mass of the gas remains the same.
B.
The pressure of the gas increases.
of momentum on collision with the
C.
The number of the molecules per unit
walls of the container.
volume increases.
E.
The molecules suffer negligible change
AL-MC-Gas / p.2
6.
(88-I-19)
The mean free path of air molecules is equal to
A.
the average diameter of an air
molecule.
B.
the average separation between air
molecule.
C.
the average distance between collisions
of air molecules.
D.
the average distance traveled by an air
A.
P0 .
B.
T P0 / T0 .
C.
T0 P0 /T.
D.
2T P0 /(T + T0 )
E.
P0 (T + T0 )/2 T0 .
molecule in unit time.
E.
the distance traveled by an air
9.
(89-I-17)
molecule in free space before coming
Two different gases A and B are contained in two
to rest.
identical vessels. If the ratio of their molecular
masses and absolute temperatures are respectively
7.
(88-I-20)
8 : 1 and 2 : 1, the ratio of their r.m.s. molecular
An inexpansible vessel contains 1.2 kg of gas at
speeds will be
300 K. What is the mass of gas expelled from the
vessel if it is heated from 300 K to 400 K under
A.
1 : 4.
constant pressure?
B.
1 : 2.
C.
1 : 1.
A.
0.25 kg
D.
2 : 1.
B.
0.3 kg
E.
4 : 1.
C.
0.6 kg
D.
0.75 kg
E.
0.9 kg
10.
(89-I-18)
The internal energy of an ideal gas at temperature
T is 3 CT/2, where C is a constant. Given that R =
8.
(89-I-16)
Two vessels of equal volume both contain an ideal
the molar gas constant,
gas and are connected by a tube of negligible
k = Boltzmann constant, then for an ideal gas
volume. Initially both vessels are at temperature
containing N molecules, the constant C is equal to
T0 and pressure P0 , One vessel is maintained at
A.
N A R.
B.
N A k.
C.
NR/ N A .
D.
Nk/ N A .
E.
NR.
T0 , while the temperature of the other is raised to
T. The new pressure is then given by
AL-MC-Gas / p.3
11.
(90-I-13)
13.
Container X holds pure hydrogen gas while
(91-I-17)
A fixed mass of ideal gas at S.T.P. occupies a
container Y holds pure oxygen gas. If the
volume of
hydrogen molecules in X have the same r.m.s.
speed as the oxygen molecules in Y, which of
2 m3 . The gas is heated and allowed
to expand to a final volume of
the following conclusions may be drawn?
4 m3 with its
pressure doubled. The root mean square speed of
A.
The gas in X has a higher
the gas molecules is
temperature than Y.
B.
C.
D.
The gas in X has a higher pressure
A.
reduced to one quarter of its value.
than Y.
B.
halved.
The gas in Y has a higher
C.
unchanged.
temperature than X.
D.
doubled.
The gas in Y has a higher pressure
E.
increased four times.
than X.
E.
The gases in X and Y are at the
same temperature.
14.
(91-I-18)
An ideal gas is taken through the series of changes
shown.
12.
(91-I-10)
Which of the following properties of molecules of
an ideal gas is/are the same on the moon as on the
earth, if the temperature and volume of the gas are
unchanged?
(1)
The average momentum change when a
molecule of the gas rebounds from a wall of
the container.
(2)
The average kinetic energy of a molecule of
the gas.
(3)
Which of the following statements is/are correct?
The weight of a molecule of the gas.
(1)
No net work is done by the gas in completing
A.
(1), (2) and (3)
one cycle.
B.
(1) and (2) only
C.
(2) and (3) only
AB is equal to that done on the gas during
D.
(1) only
the change CD.
E.
(3) only
(2)
(3)
The work done by the gas during the change
The gas has the same temperature at B and at
C.
A. (1), (2) and (3)
B. (1) and (2) only
C. (2) and (3) only
D. (1) only
E. (3) only
AL-MC-Gas / p.4
15.
(91-I-19)
17.
(92-I-14)
Which of the following statements about an
The relative atomic mass of oxygen is 16. What is
experiment showing the Brownian motion with
the ratio of the average speed of oxygen molecules
smoke particles in air is/are correct?
to that of hydrogen molecules at room
temperature?
(1)
(2)
(3)
The motion is caused by collisions between
air molecules and smoke particles.
A.
1/16
The experiment makes it possible to see the
B.
1/4
motion of the air molecules.
C.
1
The motion is irregular because air is a
D.
4
mixture of gases, and the molecules have
E.
16
different masses.
18
A. (1), (2) and (3)
Which of the graphs best represents the
B. (1) and (2) only
distribution of molecular speeds in a gas at 500 K
C. (2) and (3) only
if the dotted curve represents this distribution for
D. (1) only
the same gas at 300 K?
E. (3) only
16.
(92-I-15)
(92-I-13)
Given : Avogadro constant = 6  10 mol
23
1
JK 1
1
1
Molar gas constant = 8.31Jmol K
Boltzmann constant = 1.38  10
23
If 1 mole of an ideal gas is heated under constant
pressure from 20oC to 70 oC, the total kinetic
energy of the gas molecules is increased by
A.
208 J
B.
415 J
C.
581 J
D.
623 J
E.
831 J
AL-MC-Gas / p.5
19.
(93-I-16)
21.
An ideal gas is contained in a cylinder fitted with a
(93-I-18)
Identical containers A and B contain oxygen ( O2 )
light pistons as shown below :
and hydrogen ( H 2 ) respectively.
Initially, the piston is held fixed and the gas is
cooled. Afterwards, the piston is pushed inwards
slowly. Which of the following graphs represents
the variation of gas pressure P with gas volume V?
Both gases are at room temperature and
(i represents initial state; f represents final state)
atmospheric pressure. Which of the following
statements is/are true?
In both containers,
(1)
the number of gas molecules is the same;
(2)
the r.m.s. speed of gas molecules is the same;
(3)
the frequency of collision of gas molecules
with the walls of container is the same.
20.
A.
(1) only
B.
(3) only
C.
(1) and (2) only
D.
(2) and (3) only
E.
(1), (2) and (3)
(93-I-17)
o
An inexpansible vessel contains air at 50 C .
What percentage of air remains in the vessel if it is
o
heated to 100 C under constant pressure? (You
may take the ice point to be 273 K)
22.
(93-I-20)
If the diameter of an air molecule is d, which of the
following gives correct estimates of the average
separation of air molecules and their mean free
path under atmospheric pressure?
A.
87 %
B.
85 %
Average separation
Mean free
C.
73 %
of air molecules
path
D.
63 %
E.
50 %
A.
d
10d
B.
10d
10d
C.
10d
100d
D.
100d
10d
E.
100d
100d
AL-MC-Gas / p.6
23.
(95-IIA-20)
26.
(97-IIA-36)
The pressure of an ideal gas in a container is P. If
A fixed mass of an ideal gas undergoes a cycle
the number of gas molecules is halved, the volume
ABCD in which its pressure p and volume V as
of the container is doubled and the temperature is
shown in the p-V diagram below.
kept constant, the pressure will be
A.
P/4
B.
P/2
C.
P
D.
2P
E.
4P
Which of the following statements is/are correct?
24.
(95-IIA-21)
The r.m.s. speed of the molecules of a certain gas
(1)
From A to B, work is done by the gas.
X is 341 ms at 298 K. Find the molar mass of the
(2)
From B to C, heat is extracted from the gas.
gas X. (Given : Universal gas constant
(3)
From C to D, the internal energy of the gas
-1
1
R = 8.31Jmol K
25.
1
increases.
)
A.
5.4 g
A.
(1) only
B.
21.8 g
B.
(3) only
C.
33.8 g
C.
(1) and (2) only
D.
42.6 g
D.
(2) and (3) only
E.
63.9 g
E.
(1), (2) and (3)
(97-IIA-35)
27.
(97-IIA-37)
Two different ideal gases, A and B, are contained
When a gas is below its critical temperature, which
in two identical vessels. If the ratio of their
of the following is/are correct?
absolute temperature and ratio of the
root-mean-square speed of the molecules are
(1)
Intermolecular forces are significant.
respectively 2 : 1 and 3 : 1, the ratio of their
(2)
The gas can be liquefied by applying
molecular mass is
pressure alone.
(3)
Collisions between molecules are not
A.
2:3
perfectly elastic.
B.
2:9
C.
1:6
A.
(1) only
D.
9:2
B.
(3) only
E.
3:2
C.
(1) and (2) only
D.
(2) and (3) only
E.
(1), (2) and (3)
AL-MC-Gas / p.7
28.
(98-IIA-33)
30.
(99-IIA-37)
The internal energy of an ideal gas always changes
when
(1)
its volume increases.
(2)
it undergoes an isothermal change.
(3)
it is compressed in an insulating container.
Two metallic containers X and Y of volume V and
4V respectively are connected by a narrow tube as
A. (1) only
shown. Initially the tap S is closed and an ideal gas
B. (3) only
is contained in X at a pressure of 400 kPa while
C. (1) and (2) only
container Y is evacuated. The tap S is then opened
D. (2) and (3) only
and when equilibrium is finally reached
E. (1), (2) and (3)
29.
(98-IIA-35)
A.
the gas pressure in X is 100 kPa
B.
there are still gas molecules moving
The root-mean-square speed of a sample of helium
through the tap S.
gas molecules, each of mass m, is c. Which of the
C.
following deductions is correct?
the gas in X is equal to that in Y.
D.
A.
The percentage of molecules travelling
E.
speeds.
D.
Half of the molecules travel at a speed
31.
(99-IIA-38)
All molecules travel randomly with
Which of the following descriptions about ideal
speed c.
gas is/are correct?
The average speed of the molecules is
c.
E.
the gas molecules in Y on average
move faster than those in X.
higher than c
C.
the density of gas molecules in X is
greater than that in Y.
at speed c is greater than at other
B.
the product of pressure and volume of
(1)
The average kinetic energy of the
molecules is
1 mc 2 .
2
An ideal gas obeys Boyle’s law only under
high temperature and low pressure.
(2)
The molecules of an ideal gas have no size.
(3)
The internal energy of an ideal gas consists
of kinetic energy only.
A.
(1) only
B.
(3) only
C.
(1) and (2) only
D.
(2) and (3) only
E.
(1), (2) and (3)
AL-MC-Gas / p.8
32.
(99-IIA-39)
34.
(00-IIA-39)
Which of the following statements concerning a
real gas is/are correct?
(1)
Collisions between molecules and the wall of
a container are not perfectly elastic.
(2)
The volume of the molecules cannot be
neglected.
A fixed mass of an ideal gas undergoes the process
(3)
Intermolecular forces cannot be neglected.
ABC as shown in the pressure-temperature diagram.
Which of the following deductions from the
A.
(1) only
diagram is incorrect?
B.
(2) only
C.
(3) only
D.
(1) and (2) only
E.
(2) and (3) only
A. The volume of the gas at C is greater
than that at B.
B. No work is done by the gas when it
changes from A to B.
C. Work is done by the gas on the
surroundings when it changes from B to
35.
(01-IIA-32)
Which of the following is NOT a basic assumption
of the kinetic theory of an ideal gas ?
C.
D. Heat energy is transferred to the gas
when it changes from A to B.
A.
All molecules are in random motion.
B.
All molecules move with the same
E. Heat energy is extracted from the gas
when it changes from B to C.
speed at a certain temperature.
C.
All molecules are point particles that
have no physical size.
33.
(00-IIA-38)
D.
All collisions are perfectly elastic.
E.
All molecules do not exert force on
one another except during collisions.
A fixed mass of an ideal gas goes through the three
processes from P to S indicated in the above p-T
diagram : (1) : P  Q, (2) : Q  R, (3) : R  S.
During which of the above processes is work done
by the gas on the surroundings?
A.
(1) only
B.
(3) only
C.
(1) and (2) only
D.
(1) and (3) only
E.
(2) and (3) only
AL-MC-Gas / p.9
36.
(02-II-38)
39.
(03-IIA-37)
The graph shows the relation between the pressure
P and the absolute temperature T of a fixed mass of
an ideal gas, which changes from state A to state B
along the path AB. Which of the following
statement is/are correct?
(1)
The
graph
shows
that
P
is
directly
proportional T
(2)
The volume V of gas increases.
(3)
All the points on straight line AB satisfy the
relation
PV
 constant
T
A fixed mass of an ideal gas is contained in a
cylinder with a light piston. In which of the
following processes will the internal energy of
the gas increase?
(1)
A.
(1) only
B.
(3) only
C.
(1) and (2) only
D.
(2) and (3) only
(2)
(3)
37.
(02-II-39)
What is the order of magnitude of the number of
The gas is made to expand under
constant pressure.
The gas pressure is increased while
keeping the piston at a fixed
position.
The gas is compressed suddenly so
that heat transfer to or from the gas
is negligible.
molecules in 1 cm3of air in an atmospheric
pressure of 105 Pa and at room temperature?
(Given: Universal gas
1
constant  8.31JK mol
1
Avogadro constant  6.02  10 mol
23
A.
B.
C.
D.
1
10 25
1019
1016
1013
A.
B.
C.
D.
(1) and (2) only
(1) and (3) only
(2) and (3) only
(1), (2) and (3)
40. (04-IIA-14)
Given:
Atmospheric pressure near earth’s
surface=100kPa
Density if air near the earth’s surface
38.
=1.3 kgm-3
(02-II-40)

At 80 C, the r.m.s speed of the molecules in a
fixed mass of ideal gas is c. If the temperature is

increased to 160 C, the r.m.s speed of the gas
molecules would become
Which of the following is the best estimate for the
total mass of the earth’s atmosphere?
A.
5 x 1012kg
B.
5 x 1015kg
A.
2c
C.
5 x 1018kg
B.
1.4 c
D.
5 x 1021kg
C.
1.2 c
D.
1.1 c
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