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1. The kinetic theory of gases assumes that molecules of a gas are
A. In random, continuous motion
B. Stationary at fixed positions
C. Arranged in an ordered lattice
D. Moving only along straight parallel lines
Answer: A. In random, continuous motion
Explanation: Kinetic theory assumes gas molecules are in constant, random motion, colliding with each other and the container walls.
2. According to kinetic theory, collisions between gas molecules are assumed to be
A. Perfectly elastic
B. Perfectly inelastic
C. Partially elastic
D. Non-existent
Answer: A. Perfectly elastic
Explanation: Kinetic theory assumes that molecular collisions, both between molecules and with the walls, are perfectly elastic, conserving kinetic energy.
3. An ideal gas obeys the equation of state
A. PV = nRT
B. PV = nR/T
C. P/V = nRT
D. PV² = nRT
Answer: A. PV = nRT
Explanation: The ideal gas equation PV = nRT relates pressure, volume, number of moles, gas constant, and absolute temperature for an ideal gas.
4. Boyle's law states that at constant temperature, the pressure of a given mass of gas is
A. Inversely proportional to its volume
B. Directly proportional to its volume
C. Independent of its volume
D. Proportional to the square of its volume
Answer: A. Inversely proportional to its volume
Explanation: Boyle's law states that PV = constant at constant temperature, so pressure is inversely proportional to volume.
5. Charles's law states that at constant pressure, the volume of a given mass of gas is
A. Directly proportional to its absolute temperature
B. Inversely proportional to its absolute temperature
C. Independent of temperature
D. Proportional to the square of temperature
Answer: A. Directly proportional to its absolute temperature
Explanation: Charles's law states V/T = constant at constant pressure, meaning volume is directly proportional to absolute temperature.
6. Avogadro's law states that equal volumes of all gases, at the same temperature and pressure, contain
A. Equal numbers of molecules
B. Equal masses
C. Equal densities
D. Equal specific heats
Answer: A. Equal numbers of molecules
Explanation: Avogadro's law states that equal volumes of all ideal gases at the same temperature and pressure contain the same number of molecules.
7. Avogadro's number (number of molecules in one mole) is approximately
A. 6.022 × 10²³
B. 6.022 × 10²⁰
C. 3.011 × 10²³
D. 6.022 × 10²⁶
Answer: A. 6.022 × 10²³
Explanation: Avogadro's number is defined as approximately 6.022 × 10²³ molecules (or particles) per mole of a substance.
8. According to kinetic theory, the pressure exerted by a gas is due to
A. Continuous collisions of gas molecules with the walls of the container
B. Gravitational attraction between molecules
C. Chemical reactions between molecules
D. Molecules sticking to the container walls
Answer: A. Continuous collisions of gas molecules with the walls of the container
Explanation: Pressure arises from the continual bombardment and momentum transfer of gas molecules colliding elastically with the container walls.
9. The average kinetic energy of a gas molecule is directly proportional to
A. The absolute temperature of the gas
B. The pressure of the gas
C. The volume of the container
D. The molar mass of the gas
Answer: A. The absolute temperature of the gas
Explanation: According to kinetic theory, the average translational kinetic energy per molecule is (3/2)kT, directly proportional to the absolute temperature.
10. The rms (root mean square) speed of gas molecules is proportional to
A. The square root of absolute temperature
B. The absolute temperature directly
C. The square of absolute temperature
D. The inverse of absolute temperature
Answer: A. The square root of absolute temperature
Explanation: The rms speed is given by v_rms = √(3RT/M), so it is proportional to the square root of the absolute temperature.
11. At the same temperature, lighter gas molecules move ___ than heavier gas molecules.
A. Faster
B. Slower
C. At the same speed
D. Not at all
Answer: A. Faster
Explanation: Since v_rms is inversely proportional to the square root of molar mass, lighter molecules like hydrogen move faster than heavier molecules like oxygen at the same temperature.
12. At absolute zero temperature, the kinetic energy of gas molecules (as per classical kinetic theory) is
A. Zero
B. Maximum
C. Equal to Avogadro's number
D. Infinite
Answer: A. Zero
Explanation: Since average kinetic energy is proportional to absolute temperature, at T = 0 K, the kinetic energy of gas molecules becomes zero according to classical kinetic theory.
13. The number of degrees of freedom of a monoatomic gas molecule is
A. 3
B. 5
C. 6
D. 7
Answer: A. 3
Explanation: A monoatomic gas molecule has only 3 translational degrees of freedom (along the x, y, and z axes), with no rotational or vibrational modes considered.
14. The number of degrees of freedom of a diatomic gas molecule (ignoring vibration) is
A. 5
B. 3
C. 6
D. 7
Answer: A. 5
Explanation: A diatomic molecule has 3 translational and 2 rotational degrees of freedom (excluding vibration), totaling 5 degrees of freedom.
15. The law of equipartition of energy states that in thermal equilibrium, energy is distributed
A. Equally among all degrees of freedom, each getting (1/2)kT
B. Only among translational degrees of freedom
C. Unequally, with more energy given to rotational modes
D. Entirely to potential energy
Answer: A. Equally among all degrees of freedom, each getting (1/2)kT
Explanation: The law of equipartition of energy states that in thermal equilibrium, the total energy is equally distributed among all degrees of freedom, with each contributing (1/2)kT per molecule.
16. The average distance a molecule travels between two successive collisions is called
A. Mean free path
B. Molecular diameter
C. Mean square speed
D. Molecular range
Answer: A. Mean free path
Explanation: The mean free path is the average distance traveled by a gas molecule between two successive collisions with other molecules.
17. As the pressure of a gas increases at constant temperature, the mean free path
A. Decreases
B. Increases
C. Remains constant
D. Becomes infinite
Answer: A. Decreases
Explanation: Increasing pressure increases the number density of molecules, leading to more frequent collisions and hence a shorter mean free path.
18. Which of the following gas laws can be combined to derive the ideal gas equation PV = nRT?
A. Boyle's law, Charles's law, and Avogadro's law
B. Only Boyle's law
C. Only Newton's laws of motion
D. Only Avogadro's law
Answer: A. Boyle's law, Charles's law, and Avogadro's law
Explanation: The ideal gas equation PV = nRT combines Boyle's law, Charles's law (also called Gay-Lussac's law variant), and Avogadro's law into a single relation.
19. Real gases deviate from ideal gas behavior mainly at
A. High pressure and low temperature
B. Low pressure and high temperature
C. Standard temperature and pressure only
D. Absolute zero pressure
Answer: A. High pressure and low temperature
Explanation: At high pressure and low temperature, intermolecular forces and finite molecular volume become significant, causing real gases to deviate from ideal gas behavior.
20. Brownian motion of suspended particles in a fluid provides evidence for
A. The random, continuous motion of molecules
B. The existence of atoms only in solids
C. Perfectly ordered molecular motion
D. Absence of intermolecular collisions
Answer: A. The random, continuous motion of molecules
Explanation: Brownian motion, the erratic movement of small suspended particles, results from random collisions with fluid molecules and supports the kinetic theory's assumption of ceaseless molecular motion.
21. The pressure of an ideal gas, according to kinetic theory, is given by P = (1/3)ρv²(rms), where ρ is
A. Density of the gas
B. Number of molecules
C. Volume of the gas
D. Molar mass of the gas
Answer: A. Density of the gas
Explanation: In the kinetic theory expression P = (1/3)ρv²(rms), ρ represents the density (mass per unit volume) of the gas.
22. If the absolute temperature of a gas is doubled, keeping volume constant, its pressure
A. Doubles
B. Remains the same
C. Becomes half
D. Becomes four times
Answer: A. Doubles
Explanation: By the ideal gas law at constant volume (Gay-Lussac's law), pressure is directly proportional to absolute temperature, so doubling T doubles P.
23. For a mixture of non-reacting ideal gases, the total pressure is the sum of the pressures each gas would exert alone. This is
A. Dalton's law of partial pressures
B. Boyle's law
C. Avogadro's law
D. Charles's law
Answer: A. Dalton's law of partial pressures
Explanation: Dalton's law of partial pressures states that the total pressure exerted by a mixture of non-reacting gases equals the sum of the partial pressures of individual gases.
24. Why does a balloon expand when heated?
A. Molecules move faster and collide more forcefully, increasing pressure that expands the balloon
B. The rubber material shrinks with heat
C. Gas molecules disappear when heated
D. Heating decreases the number of gas molecules
Answer: A. Molecules move faster and collide more forcefully, increasing pressure that expands the balloon
Explanation: Heating increases the average kinetic energy and speed of gas molecules, causing more frequent and forceful collisions with the balloon walls, increasing pressure and expanding the balloon until equilibrium is restored.
25. The specific heat ratio γ = Cp/Cv for a monoatomic ideal gas is
A. 5/3
B. 7/5
C. 4/3
D. 1
Answer: A. 5/3
Explanation: For a monoatomic gas with 3 degrees of freedom, Cv = (3/2)R and Cp = (5/2)R, giving γ = Cp/Cv = 5/3.
26. The specific heat ratio γ for a diatomic ideal gas (excluding vibration) is
A. 7/5
B. 5/3
C. 9/7
D. 3/2
Answer: A. 7/5
Explanation: A diatomic gas has 5 degrees of freedom (excluding vibration), giving Cv = (5/2)R and Cp = (7/2)R, so γ = 7/5.
27. Why do bicycle or car tyres burst more often in summer than in winter?
A. Higher temperature increases the air pressure inside the tyre beyond its safe limit
B. Rubber becomes thinner in summer
C. Air molecules leave the tyre faster in summer
D. Tyres lose elasticity only in cold weather
Answer: A. Higher temperature increases the air pressure inside the tyre beyond its safe limit
Explanation: In summer, higher ambient temperature raises the kinetic energy of air molecules inside the tyre, increasing internal pressure at constant volume, which can exceed the tyre's rated limit and cause a burst.
28. According to kinetic theory, the size of gas molecules is assumed to be
A. Negligible compared to the distance between them
B. Equal to the size of the container
C. Larger than the mean free path
D. Increasing with temperature
Answer: A. Negligible compared to the distance between them
Explanation: Kinetic theory assumes that the actual volume occupied by gas molecules is negligible compared to the volume of the container, treating them essentially as point masses.
29. If the volume of a fixed mass of gas is reduced to half at constant temperature, its pressure becomes
A. Double
B. Half
C. The same
D. Four times
Answer: A. Double
Explanation: By Boyle's law, at constant temperature, pressure is inversely proportional to volume, so halving the volume doubles the pressure.
30. Two different ideal gases at the same temperature have
A. The same average kinetic energy per molecule
B. The same rms speed
C. The same pressure regardless of volume
D. The same mean free path
Answer: A. The same average kinetic energy per molecule
Explanation: Since average kinetic energy per molecule, (3/2)kT, depends only on absolute temperature and not on the type of gas, two different gases at the same temperature have equal average kinetic energy per molecule, even though their rms speeds differ due to different molar masses.
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