EWT | Academic Question

Questions
Question (1)
QN0038345

Two vessels separately contain two ideal gases  and  at the same temperature. The pressure of  being twice that of . Under such conditions, the density of  is found to be 1.5 times the density of . The ratio of molecular weight of  and  is : 

  • (A)

  • (B)

    2

  • (C)

  • (D)

Correct Answer: A
Explanation:

From

and

From question,

so,

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Question (2)
QN0038346

The molecules of a given mass of a gas have r.m.s. velocity of  at  and  pressure. When the temperature and pressure of the gas are respectively,  and , the r.m.s. velocity of its molecules in  is :    

  • (A)

  • (B)

  • (C)

  • (D)

Correct Answer: B
Explanation:

Here ;

temperature

temperature  ?

R.M.S. Velocity,

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Question (3)
QN0038347

A gas mixture consists of 2 moles of  and 4 moles of  at temperature T. Neglecting all vibrational modes, the total internal energy of the system is :

  • (A)

  • (B)

  • (C)

  • (D)

Correct Answer: C
Explanation:

Internal energy of the system is given by

Degree of freedom;

and, number of moles

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Question (4)
QN0038348

At what temperature will the rms speed of oxygen molecules become just sufficient for escaping from the Earth's atmosphere?                                                                                                   

(Given :

Mass of oxygen molecule

Boltzmann's constant  )

  • (A)

  • (B)

  • (C)

  • (D)

Correct Answer: B
Explanation:

Let at temperature  rms speed of oxygen molecules become just sufficient for escaping from the Earth's atmosphere

Also,

Putting value of  and  we get,

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Question (5)
QN0038349

Increase in temperature of a gas filled in a container would lead to:

  • (A)

    increase in its mass

  • (B)

    increase in its kinetic energy

  • (C)

    decrease in its pressure

  • (D)

    decrease in intermolecular distance

Correct Answer: B
Explanation:

As

Increase in temperature would lead to the increase in kinetic energy of gas.

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Question (6)
QN0038350

A cylinder contains hydrogen gas at pressure of  and temperature . 

Its density is :           

  • (A)

  • (B)

  • (C)

  • (D)

Correct Answer: A
Explanation:

Given : Pressure

Mass of hydrogen,

Temperature,

Using, ideal gas equation,

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Question (7)
QN0038351

The mean free path for a gas, with molecular diameter  and number density  can be expressed as :

  • (A)

  • (B)

  • (C)

  • (D)

Correct Answer: A
Explanation:

Mean free path for a gas

Here,  diameter of a gas molecule and,  molecular density.

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Question (8)
QN0038352

The average thermal energy for a mono-atomic gas is :  is Boltzmann constant and , absolute temperature)

  • (A)

  • (B)

  • (C)

  • (D)

Correct Answer: A
Explanation:

From the law of equipartition of energy, energy associated with each degree of freedom is .

For monoatomic gases, degree of freedom is 3 . Hence average thermal energy for mono-atomic gas is

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Question (9)
QN0038353

Match Column - I and Column - II and choose the correct match from the given choices.

                                                                              

Column - I                                                                                            Column-II

(A) Root mean square speed of gas molecules                               (i)  

(B) Pressure exerted by ideal gas                                                         (ii)                               

(C) Average kinetic energy of a molecule                                         (iii)

(D) Total internal energy of 1 mole of a diatomic gas                  (iv)

  • (A)

    A- (iii), B - (ii), C- (i), D - (iv)

  • (B)

    A - (iii), B - (i), C - (iv), D - (ii)

  • (C)

    A - (ii), B - (iii), C - (iv), D - (i)

  • (D)

    A - (ii), B - (i), C - (iv), D - (iii)

Correct Answer: D
Explanation:

Root mean square RMS speed of gas molecule

Pressure exerted by ideal gas

Average kinetic energy of a molecule 
Total internal energy of a gas is

Here, for one mole  and

for diatomic

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Question (10)
QN0038354

The volume occupied by the molecules contained in 4.5  water of STP, if the intermolecular forces vanish away is

  • (A)

  • (B)

  • (C)

  • (D)

Correct Answer: C
Explanation:

Number of moles of water molecules (n)

[at STP, T  ]

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