# Class 11th Physics – 13 kinetic theory MCQs

#### Kinetic theory of gases provides theoretical explanation for ____.

Kinetic theory of gases provides a theoretical explanation for Boyle's law, Charle's law and also to Dalton's law of partial pressures.

#### If gas in a container is in equilibrium, the nature of the equilibrium is ____ indicating that ____

If gas in a container is in equilibrium, the nature of the equilibrium is dynamic, indicating that all molecules move with different speeds but average of speeds of all molecules is constant.

#### According to the law of equipartition of energy, the internal energy of a gas is distributed equally ____.

According to the law of equipartition of energy the internal energy of a gas is distributed equally among all possible energy modes.

#### ____ is able to explain the "law of definite proportions" and "law of multiple proportions"

Dalton's atomic theory is able to explain the "law of definite proportions" and "law of multiple proportions"

#### ____ Motion of gas molecules have modes of energy associated with both kinetic energy as well as potential energy.

Only vibrational modes of energy has equal contribution from both kinetic and potential energy.

#### At the same temperature, the rms speed is greater for ____.

At constant temperature V_{RMS} ∝1/√ M
Since molar mass for hydrogen is less than that of oxygen V_{RMS} must be greater for hydrogen.

#### At normal atmospheric temperature and pressure, hydrogen occupying 44.8 l of volume contains 2 moles of hydrogen molecules. Oxygen occupying the same volume at normal atmospheric temperature and pressure contains ____ of molecules.

At normal atmospheric temperature and pressure, hydrogen occupying 44.8 l of volume contains 2 moles of hydrogen molecules. Oxygen occupying the same volume at normal atmospheric temperature and pressure contains 2 moles of molecules. This is according to the Avogadro's hypothesis, which states that equal volumes of all gases at equal temperatures and pressures contain equal number of molecules.

#### a) According to law of definite proportions, mass of the constituents of any compound are always in a fixed proportion. b) According to law of multiple proportions, when two elements combine to form more than one compound, for a fixed mass of one element, the masses of the other elements are in the ratio of small integers.

According to law of definite proportions, mass of the constituents of any compound are always in a fixed proportion. According to law of multiple proportions, when two elements combine to form more than one compound, for a fixed mass of one element, the masses of the other elements are in the ratio of small integers.

#### The specific heat of an ideal gas is ____.

According to classical laws the specific heat capacity of an ideal gas is independent of absolute temperature of the gas.

#### When volume of a given mass of gas is reduced to half and temperature is doubled, the pressure of the gas ____.

Ideal gas equation PV = nRT

or PV/T=constant

V_{2}=V_{1}/2

T_{2}=2T_{1}

P_{2}=?

P_{1}V_{1}/T_{1}=P_{2}V_{2}/T_{2}

P_{2}=(T_{2}/T_{1})P_{1}

= (2) (2) P_{1}

= 4P_{1}

#### The expression for pressure exerted by a gas P=1/3m N v^{2} is applicable for ____.

Though for deriving the expression, a cubical container is assumed for simplicity, however the expressions is true for containers of any shape.

#### Keeping all other things constant, if average speed of molecules of a gas in a container is doubled, the pressure of the gas ____.

Pressure P=13nmv^{2}

Since P ∝ v^{2},

If 'v' is doubled, pressure is quadrupled.

#### According to the kinetic theory of gases, ____is/are conserved in collisions among gas molecules or between molecules and the walls of the container.

According to the kinetic theory of gases, collisions among the gas molecules or between molecules, and the walls of the container, are elastic in nature. Hence, in such collisions, both the linear momentum and the kinetic energy are conserved.

#### If the ratio of the rates of diffusion of the two gases is 4:1, then the ratio of their densities is ____.

Rate of diffusion 'r' is inversely proportional to square root of density
r∝1/√ d
d_{1}:d_{2}=r_{2}^{2}:r_{1}^{2} = 1 : 16

#### a) Smallest constituents of an element are atoms. b) Atom is indivisible

Smallest constituents of an element are atoms. Though Dalton proposed that atoms are indivisible. But subsequently it is found that they consist of smaller particles like proton, electron and neutrons.

#### The ratio of mass of hydrogen to mass of oxygen in a water molecule of river water is ____ the ratio of mass of hydrogen to mass of oxygen in water molecule of sea water.

According to law of definite proportions, the ratio of mass of hydrogen to mass of oxygen in a water molecule of river water is equal to the ratio of mass of hydrogen to mass of oxygen in water molecule of sea water.

#### If the temperature of the gas is doubled, the average translational energy of a monatomic gas molecule ____.

The average translational energy of a monatomic gas molecule

E_{T}=3/2K_{B}T

that means, E_{T} ∝ T

If 'T' is doubled, "E_{T}" also gets doubled.

#### Molecules of a monoatomic gas have ____ degrees of freedom.

Molecules of a monoatomic gas have three degrees of freedom.

#### Under ____ conditions a real gas obeys ideal gas equation PV = μ R T.

Under very high temperature and low pressure conditions, a real gas obeys ideal gas equation.

#### Interatomic forces are negligible in case of ____

Interatomic forces are negligible in case of gases

#### At constant temperature, the density of gas 'P' is three times that of gas 'Q'. If molar mass of gas 'Q' is twice that of 'P', the ratio of pressure of 'P' to pressure of Q is ____.

ρ_{P }= 3 ρ_{Q }

M_{Q }= 2M_{P}

According to ideal gas equation P=ρRT/M_{O}

At constant temperature,

(P_{P}:P_{Q})=(ρ_{P}:ρ_{Q})(M_{Q}:M_{P})
= (3) (2) = 6 : 1

#### A mixture of 64 g of oxygen and 5g of hydrogen is kept in a container at N.T.P. the volume of the container is ____.

Gram molecular weight of Oxygen is '32 g' and of hydrogen is '2g'

At NTP, 64 g of oxygen occupies 2 × 22.4 lt = 44.8 litre

5g of hydrogen occupies 2.5 × 22.4 lt = 56 litre

Together the mixture occupies 100.8 litre

#### An ideal gas at 27°C is heated at constant pressure. If the volume of the gas is now four times its initial volume, temperature of the gas is ____.

At constant pressure V ∝ T

or V_{1}/T_{1}=V_{2}/T_{2}

or T_{2}=(V_{2}/V_{1})T_{1}

=(4) (27+273)

= 1200K

= 927°C

#### At ____ temperature the kinetic energy of a gas molecule is doubles that of its value at 27°C.

Average kinetic energy of a gas molecule K.E. = 3/2K_{B}T

K_{1}/K_{2}=T_{1}/T_{2}

T_{2}= (K_{2}/K_{1}).T_{1}

= 2 × 300 = 600 K (Since K_{2} = 2K_{1})

= 327°C

#### If degree of freedom of a gas is "f", 'γ' for the gas is ____.

γ=C_{p}/C_{v}=1+(2/f)

#### When the number of molecules per unit volume is 'N', the pressure exerted by oxygen at certain temperature is 'P'. By keeping the temperature constant, if the number of molecules per unit volume is doubled, the pressure of the gas is ____.

Pressure P=1/3m N v^{2}

If the gas and its temperature is same, then P ∝ N

If 'N' is doubled then 'P' is also doubled.

#### Kinetic energy of one gm-mole of a gas at normal temperature and pressure is ____. (R = 8.31 Jmol^{-1K-1})

Average kinetic energy of one mole of a gas = (3/2)RT
=3/2×8.31×273
3.4 × 10^{3}J

#### It is given that 'γ' for a gas is '7/5', then the gas could be ____.

The ratio of C_{P} to C_{V} is 1.4 or 7/5 for a diatomic molecule. From the given list only hydrogen is the diatomic molecule.

#### A mixture of Hydrogen and Helium gases in a container is at a temperature of 300 K. Then average kinetic energy of Helium is____.

Since kinetic energy of a gas depends only on the temperature of the gas, the average kinetic energy of helium is same as the average kinetic energy of hydrogen as both are at the same temperature 300 K.

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