Kinetic Theory Of Gases(12th Grade > Physics ) Questions and answers for exam Preparation

12th Grade > Physics

KINETIC THEORY OF GASES MCQs

Total Questions : 24 | Page 2 of 3 pages

Question 11. A system which exchanges both matter & energy with the surrounding is called a closed system.

True
False
Closed system
None

Discuss Question

Answer: Option B. -> False
:
B
A system which exchanges both matter & energy with the surroundings is called an open system by definition.
Open system -matter and energy both can be transferred.
Closed system - Only energy can be transferred.
Isolated - Neither energy nor matter can be transferred.

Question 12. Find the value of

Δ U

+20 J
-80 J
+80 J
-20 J

Discuss Question

Answer: Option B. -> -80 J
:
B
Take a minute and try to get this on your own. Then move on the next video for the explanation.

Question 13. Fundamental properties which determine the state of a system are referred to as state variables.

True
False
Closed system
None

Discuss Question

Answer: Option A. -> True
:
A
Fundamental properties which determine the state of a system are referred to as state variables or state functions or thermodynamic parameters. The change in the state properties depends only on the initial and final states of the system, but is independent of the manner in which the change has been brought about. In other words, the state properties do ont depend upon the path taken.

Question 14. The Bat Life: What can be said with 100% confidence about the temperatures at point

P_{1} a n d P_{2}

TP1=TP2
TP1 > TP2
TP1 < TP2
TP1≠TP2.

Discuss Question

Answer: Option D. -> TP1≠TP2.
:
D
Just like a single macroscopic pressure being undefined for a gas which is not in equilibrium, a single macroscopic temperature is also undefined. So the temperature at

P_{1} a n d P_{2}

need not necessarily be the same, and most likely wouldn't be the same.

Question 15. An air bubble doubles its radius on raising from the bottom of water reservoir to be the surface of water in it. If the atmospheric pressure is equal to 10 m of water, the height of water in the reservoir is

10 m
20 m
70 m
80 m

Discuss Question

Answer: Option C. -> 70 m
:
C
Accoding to Boyle's law

(P_{1} V_{1})_{b o t t o m}

(P_{2} V_{2})_{t o p}

(10 + h)

\times

\frac{4}{3} π {r_{1}}^{3}

= 10

\times

\frac{4}{3} π {r_{2}}^{3}

but

r_{2} = 2 r_{1}

∴

(10 + h)

{r_{1}}^{3}

= 10

\times

{r_{1}}^{3}

∴

10 + h = 80

∴

h = 70 m

Question 16. The energy of a gas per litre is 300 joules, then its pressure will be

3 ×105Nm2
6 ×105Nm2
105Nm2
2 ×105Nm2

Discuss Question

Answer: Option D. -> 2 ×105Nm2
:
D
Energy = 300 J/litre = 300

\times 10^{3} J / m^{3}

\frac{2}{3} E = \frac{2 \times 300 \times 10^{3}}{3}

= 2

\times 10^{5} N / m^{2}

Question 17. A cylinder of fixed capacity 44.8 litre. contains a monatomic gas at standard temperature and pressure. The amount of heat required to increse the temperature of cylinder by

10^{\circ}

C will be. (R = universal gas constant)

Discuss Question

Answer: Option D. -> 30R
:
D
As we know 1 mol of any ideal gas at STP occupies a volume of 22.4 liters.
Hence number of moles of gas

μ = \frac{44.8}{22.4}

= 2
Since the volume of cylinder is fixed,
Hence

(△ Q)_{V}

μ (C_{V}) △ T = 2 \times \frac{3}{2} R \times 10

= 30R(

∵ (C_{V})_{m o n o} = \frac{3 R}{2}

))

Question 18. An enclosure of volume

V

contains a mixture of

8 g

of oxygen,

14 g

of nitrogen and

22 g

of carbon- dioxide at absolute temperature

T

. The pressure of the mixture of gases is (

R

is universal gas constant)

RTV
3RT2V
5RT4V
7RT5V

Discuss Question

Answer: Option C. -> 5RT4V
:
C
The pressure exerted by a gas is given by

P = \frac{n R T}{V}

\frac{m a s s}{m o l e c u l a r w e i g h t} \times \frac{R T}{V}

Pressure exerted by oxygen

P_{1} = \frac{8}{32} \frac{R T}{V} = \frac{1}{4} \frac{R T}{V}

Pressure exerted by oxygen

P_{2} = \frac{14}{28} \frac{R T}{V} = \frac{1}{2} \frac{R T}{V}

Pressure exerted by carbon dioxide

P_{3} = \frac{22}{44} \frac{R T}{V} = \frac{1}{2} \frac{R T}{V}

From Dalton's law of partial pressures, the total pressure exerted by the mixture is given by

P = P_{1} + P_{2} + P_{3}

\frac{1}{4} \frac{R T}{V} + \frac{1}{2} \frac{R T}{V} + \frac{1}{2} \frac{R T}{V}

\frac{5 R T}{4 V}

,
which is choice (c)

Question 19. If pressure of

C O_{2}

(real gas) in a container is given by P =

\frac{R T}{2 V - b} - \frac{a}{4 V^{2}}

then mass of the gas in container is

11 gm
22 gm
33 gm
44 gm

Discuss Question

Answer: Option B. -> 22 gm
:
B
Vander wal's gas equation for

μ

mole of real gas
(P +

\frac{μ^{2} α}{V^{2}}

)(V -

μ

b) =

μ

\Rightarrow

P =

\frac{μ R T}{V - μ b} - \frac{μ^{2}}{V^{2}}

on comparing the given equation with this standard equation we get

μ = \frac{1}{2}

. Hence

μ

\frac{m}{M} \Rightarrow

mass of gas
m =

μ M

\frac{1}{2} \times 44

= 22gm

Question 20. The ratio of two specific heats

\frac{C_{p}}{C_{v}}

of CO is

1.33
1.40
1.29
1.66

Discuss Question

Answer: Option B. -> 1.40
:
B
CO is diatomic gas, for diatomic gas

C_{p} = \frac{7}{2} R

and

C_{v} = \frac{5}{2} R \Rightarrow γ = \frac{C_{p}}{C_{v}} = \frac{\frac{7 R}{2}}{\frac{5 R}{2}}

= 1.4

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