Molecular Theory of gases - Physics II - For HSC Part 2 / XII / Class 12 (Science Group) - Section A - Multiple Choice Questions, Fill In The Blanks, Key Formulae & Concept Map

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Unit 15: Molecular Theory of gases
Physics II -
For HSC Part 2 / XII / Class 12 (Science Group)

SECTION A
Multiple Choice Questions (MCQs)

Choose the correct answer:
1. The relationship between temperature and average kinetic energy of particles in a gas is:
(a) temperature is inversely proportional to average kinetic energy
(b) temperature is directly proportional to average kinetic energy ✔
(c) temperature is independent of average kinetic energy
(d) temperature is proportional to the square of average kinetic energy

2. Standard conditions of temperature and pressure (STP) refer to a gas at:
(a) 0 °C and 1 atm ✔
(b) 20 °C and 1 atm
(c) 25 °C and 1 atm
(d) 30 °C and 101.3 kPa (1 atm)

3. If the temperature is kept constant and the volume of a gas is doubled, then pressure of a gas is:
(a) Reduced to ¹/₂ of the original value. ✔
(b) Doubled
(c) Reduced to ¹/₄ of the original value
(d) Quadrupled

4. The Avogadro's number is the number of molecules in:
(a) One mole of a substance ✔
(b) One kg of a substance
(c) One m³ of a gas
(d) One kilogram of hydrogen gas

5. Mean translational K.E. per molecule of an ideal gas at temperature T is:
(a)  ³/₂ kT ✔
(b) ¹/₂ kT
(c) ²/₃ kT
(d) kT⁴

6. The normal human body temperature is:
(a) 98.6 °F (37°C) ✔
(b) 99.6 °F (37.4 °C)
(c) 100.4 °F (38 °C)
(d) 101 °F (38.3 °C)

7. The pressure P, the density 𝝆 and the average speed of molecules of an ideal gas are related by the equation.
(a) P = ²/₃ ml²
(b) P = ¹/₃ ml²
(c) P = ¹/₃ 𝝆 V² ✔
(d) P = ²/₃ l²

8. In air at S.T.P, the average speed of the:
(a) Oxygen molecules is greater than Nitrogen molecules
(b) Nitrogen molecules is greater than Oxygen molecules
(c) Oxygen molecules is approximately equal to Nitrogen molecules
(d) Helium atoms is greater than both Oxygen and Nitrogen molecules ✔

9. If the absolute temperature of a gas is increased 3 times, the rms velocity of the molecules will be:
(a) 3 times
(b) 9 times
(c) √3 times ✔
(d) ¹/₃ times

10. A gas is enclosed in an isolated container which is placed on a fast-moving train uniformly. The temperature of the gas:
(a) Increases due to the motion of the train
(b) Decreases due to the motion of the train
(c) Remains constant ✔
(d) Fluctuates, depending on the train's speed and direction

More Multiple Choice Questions (MCQs)

TEMPERATURE
11. -459.4°F is the temperature at which. volume and pressure of the real gas becomes:
a) maximum
b) constant
c) minimum
d) zero ✔

12.The average kinetic energy of the molecules of the object is called its:
a) specific heat
b) temperature ✔
c) heat
d) hotness

13. 4.180 J of work raises the temperature of one litre of water through:
a) 1 K
b) 1 °C ✔
c) 1 °F
d) 2 °C

14. The thermal state of a body is defined by:
a) Temperature ✔
b) Heat
c) Cold
d) none of these

15. S.I. unit of temperature is:
a) Fahrenheit
b) Kelvin ✔
c) Celsius
d) Joule

16. Freezing point of water is:
a) 273 K
b) 0 °C
c) 32 °F
d) all of these ✔

17. The Fahrenheit and Kelvin scales will have the same reading when the temperature is:
a) 474.25°
b) 374.25°
c) 574.25° ✔
d) 274.25°

18. Hotness or cold of an object is expressed in terms of:
a) Heat
b) Temperature ✔
c) Thermal energy
d) Chemical energy

19. The tempeture of body shows its:
a) Physical state
b) Degree of hotness
c) Degree of coldness
d) All of these ✔

20. If heat energy is removed from an object, its temperature will normally:
a) Not change
b) Rise
c) Fall ✔
d) Fall, then rise

21. The relation between centigrade and, Fahrenheit scales of temperature is:
a) T°C = 9/5(T°F — 32)
b) T°C = 5/9(T°F + 32)
c) T°C = 5/9 (T°F — 32) ✔
d) T°F = 5/9 (T°C — 32)

22. The temperature of a normal human body is 98.6 °F. This temperature on centigrade is:
a) 0 °C
b) 37 °C ✔
c) 57 °C
d) 30 °C

23. This one of the following is the correct:
a) 1 °F < 1°C ✔
b) 1°F > 1°C
c) 1 °F = 1 °C
d) none of these

24. This one of the following is correct:
a) 1°C < IK
b) 1°C > IK
c) 1°C = IK ✔
d) none of these

25. The temperature of human body on Kelvin scale is:
a) 273 K
b) 373 K
c) 310 K ✔
d) 236 K

26. Absolute zero corresponds to this temperature on Fahrenheit scale:
a) 32 °F
b) —180 °F
c) —460 °F ✔
d) 212 °F

27. On Fahrenheit scale, the temperature of 50°C will be:
a) 40 °F
b) 10 °F
c) 122 °F ✔
d) 105 °F

28. Fahrenheit and Celsius scales of temptiqure coincide at:
a) 0°
b) 273°
c) —273°
d) —40° ✔

29. Two ends "A" & "B" of a rod are at temperature -10 °C and —30°C. The heat will flow:
a) from —30°C to —10°C
b) not at all
c) from 10°C to —30°C ✔
d) none of these

30. 273 K is equal to:
a) 0 °F
b) —32 °F
c) —273 °F
d) 32 °F ✔

31. On Celsius scale, 1°C in magnitude is equal to:
a) 32 °F
b) 16 °F
c) 0 °F
d) 1.8 °F ✔

32. The absolute temperature, corresponding to 212°F, is:
a) 485 K
b) 373 K ✔
c) 161 K
d) 100 K

KINETIC MOLECULAR THEORY OF GASES
33. The K.E. of the molecules of an ideal gas at absolute zero will be:
a) very low
b) very high
c) zero ✔
d) below zero

34. Kinetic energy of gas molecule is:
a) RT
b) ³/₂ RT
c) KT
d) ³/₂ KT ✔

35. Kinetic energy per mole of ideal gas is:
a) RT
b) ³/₂ RT ✔
c) KT
d) ³/₂ KT

36. Upon this physical quantity, Kinetic energy of gas molecules depends:
a) Temperature of gas ✔
b) Pressure of gas
c) Volume of gas
d) Nos. of moles of gas

37. The universal gas constant per molecule is called:
a) Raleigh-Jean's constant
b) Boltzman's constant ✔
c) Gas constant
d) Stefan's constant

38. At volume V and temperature T, the pressure of Nmolecules of the gas is P. If the number of molecules of the gas is doubled at constant volume, then:
a) Temperatute will become half
b) Temperature will become twice
(c) Pressure will become half
d) Pressure will become twice ✔

39. The root me speed of the molecules of an ideal gas in a sealed container is V. The gas is heated until the pressure in the container is trebled. The r.m.s. speed is now:
a) √3 V ✔
b) V/9
c) 9V
d) 3V

40. The average K.E. of the molecules of an ideal in a closed vessel is increased by a factor 4. The pressure of the gas:
a) will remain the same
b) will increase by factor of 2
c) will increase by a factor of 4 ✔
d) will increase by a factor of √2

41. A fixed mass of a gas is heated at constant volume, this one of the following will not change:
a) Temperature
b) Molecular motion
c) Internal energy
d) Density of the gas ✔

42. Pressure of an ideal gas can be written in terms of its diensity 𝝆:
a) P = 𝝆v²
b) P = ²/₃ 𝝆v²
c) P = ¹/₃ 𝝆v² ✔
b) P = ¹/₂ 𝝆v²

43. At constant temperature, the pressure P of an ideal gas is proportional to its density 𝝆 as:
a) P ∝ ¹/ _𝝆
b) P ∝ 𝝆 ✔
c) P ∝ ¹/ _𝝆²
d) P ∝ 𝝆²

44. The average translational kinetic energy of the molecules of a gas at absolute is proportional to:
a) ¹/ _T
b) T ✔
c) √T
d) T²

45. The unit of the pressure of gas is:
a) 1N/m²
b) One Pascal
c) One atmosphere
d) all of these ✔

46. According to the Kinetic theory of gases, the absolute temperature of a perfect gas is:
(a) Inversely proportional to the K.E. of the molecules
b) Independent of kinetic energy of the molecules
c) Equal to the kinetic energy of the molecules
d) Directly proportional to the average translational kinetic energy of the molecules ✔

47. The average internal energy of an ideal gas is called:
a) Pressure
b) Volume
c) Temperature ✔
d) Heat

48. A gas is enclosed in a cylinder of volume "V" pressure "P" and absolute temperature "T". If a mass of each molecule is "m" then density of gas is:
a) mK/T
b) mR/T
c) mP/KT ✔
d) mp/RT

BOYLE'S LAW, CHARLE'S LAW AND GENERAL GAS EQUATION
49. For a gas, obeying Boyle's law, if the pressure is doubled, the volume becomes:
a) Double
b) One half ✔
c) Four times
d) One fourth

50. Boyles law holds for ideal gases in:
a) isochoric process
b) isobaric process
c) isothermal process ✔
d) adiabatic process

51. If the volume, of a gas is held constiat and we increase its temperatur then:
a) Its pressure is constant
b) Its pressure rises ✔
c) Its pressure falls
d) None of these

52. The pressure exerted by a column of mercury 76cm high and 0 °C is called:
a) 1 atmosphere ✔
b) 1 Newton per square meter
c) 1 Pascal
d) Data is insufficient

53. Standard condition STP refers to a gas at:
a) 76 cm Hg 0°C
b)1 atm 273K
c) 760 mm of Hg 273K
d) All of these ✔

54. The relation between the pressure P and Volume V of fixed mass of gas at constant temperature is:
a) P/V = Constant
b) PV² constant
c) PV = Constant ✔
d) P²V = Constant

55. According to Boyle's law, the volume of a given mass of a gas is:
a) Directly proportional to the temperature
b) Directly proportional to the pressure
c) Inversely proportional to the mass
d) Inversely proportional to the Pressure at constant temperature ✔

56. The graph Boyle's. law is a:
a) Curve
b) Slope
c) Straight line
d) Hyperbola ✔

57. If the volume of a given mass of a gas is doubled wiithout changing its temperature, the pressure of the gas is:
a) Reduce to ¹/₂ of the initial value ✔
b) The same as the initial value
c) Reduced to ¹/₄ of the initial value
d) Double of the initial value

58. This one of the following curves represents Boyle's law:
59. Charles' Law states that the volume of' a given mass of gas is:
a) Inversely proportional to the absolute temperature at constant pressure
b) Directly proportional to the absolute temperature at constant pressure ✔
c) Direcily proportional to the pressure
d) Inversely proportional to the pressure

60. Charles' Law can b written mathematically as:
a) V ∝ T ✔
b) V ∝ 1/T
c) P ∝ V
d) P ∝ 1/V

61. The volume of a given gas at constant pressure becomes zero at:
a) 273 K
b) 273 °C
c) 373 K
d) -273 °C ✔

62 The. graph of Charles' law is a:
a) Curve
b) Slope
c) Straight line ✔
d) Hyperbola

63. A single equation that relates all the three variables of gas is given by:
a) PT/V = constant
b) PV/T = constant ✔
c) VT/P = constant
d) none of these

64. The ideal gas law is given in the form:
a) PV = nR /T
b) PT = NRV
c) PV = nRT ✔
d) TV = nRP

65. The value of universal gas constant `R' in S.1. unit is:
a) 8.310 J/mol K
b) 8314 J/mol K
c) 831.4 J/mol K
d) 8.314 J/mol K ✔

66. A gas which strictly obeys the laws under all conditions of temperature and pressure is:
a) Real gas
b) Ideal gas ✔
c) Permanent gas
d) Insert gas

67. At constant pressure,The volume of the given mass of a gas is V at temperature T. At this temperature, the volume of the gas will he 4V:
a) 4T ✔
b) ¹/₄ T
c) 2T
d) ¹/₂ T

68. A container is filled with a sample of an ideal gas at a pressure of 1.5 atm. The gas is compressed isothermally to one-fourth of its original volume. Its new pressure will be:
a) 2 atm
b) 4 atm
c) 6 atm ✔
d) 9 atm

Fill In The Blanks

1. Our study of Mechanics is based on the three fundamental quantities mass, length and time.
2. Temperature is a measure of the average kinetic energy of particles in a substance.
3. A temperature scale that starts at absolute zero is the theoretical lowest possible temperature. It is measured in Kelvin (K).
4. The triple point of water is the temperature (0.01°C) and pressure (611.73 Pascal's) at which water coexists in all three phases (solid, liquid, and gas).
5. If two systems are each in thermal equilibrium (equal temperature) with a third system, then the two initial systems are in thermal equilibrium with each other.
6. The general gas law states that PV = nRT, relating pressure, volume, number of moles, and temperature of a gas.
7. Boyle's Law: P₁V₁ = P₂V₂
8. According to Boyle's law Pressure and volume are inversely proportional at constant temperature.
9. Charle's Law: V₁ / T₁ = V₂ / T₂
10. According to Charle's Law Volume and temperature are directly proportional at constant pressure.
11. General Gas Law: V = nRT / P
12. According to general gas law Volume and number of moles are directly proportional at constant temperature and pressure.
13. KTG stands for Kinetic Theory of Gases.
14. Gases consist of tiny particles (molecules) that are in constant motion.
15. The molecules are very small compared to the distance between them.
16. According to Kinetic Theory Gases the molecules are in constant random motion.
17. The molecules collide with each other and the container walls.
18. Molecular movement and pressure by the equation: P = (2/3) nkT.
19. The pressure exerted by a gas is caused by the collisions of molecules with the container walls, and is related to the temperature and volume of the gas.
20. The kinetic energy of molecules is directly proportional to the temperature of the gas.
21. The kinetic energy is described by the equation KE = (3/2) kT.
22. 1 dm = 0.1m
23. 1 dm³ = 0.1m

Key Formulae

Special Thanks To Sir Wasim Ahmad
ICS Virtual Digital Coaching Center

Concept Map

Definitions To Remember

• Volume: The space occupied by a substance is called its Volume.
• Pressure: The force exerted by gas molecules on walls of vessels due to collision is called pressure.