NEETprep Bank NEET Chemistry States of Matter Questions Solved


The mean free path (λ) of a gas sample is given by:

(a) λ=2πσ2N                                (b) λ=1/2πσ2N

(c) λ=2πμσ2N                               (d) none of these

(b) A derivation for mean free path of gas.

  • If v is the velocity of the moving molecule then in one second it will collide with all moleculeswith in a distance σ between the centres.
  • In one second it sweeps a volume πσ2v where any other molecule will collide with it.
  • If n is the total number of molecules per unit volume, then nπσ2v is number of collisions a molecule suffers in one second.
  • If v is the distance traversed by molecule in one second then mean free path is given by
         λ = total distance traversed in one second /no. of collision suffered by the molecules
          =v/πσ2vn
          =1/πσ2n
  • This expression was derived with the assumption that all the molecules are at rest except the one which is colliding with the others.

 

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Which is lighter than dry air?

(a) Moist air                              (b) SO2

(c) Cl2                                      (d) O2

(a) Molar mass of moist air is lesser than dry air.

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The ratio a/b (the terms used in van der Waals' equation) has the unit:

(a) atm lire mol-1                             (b) atm dm3 mol-1

(c) dyne cm mol-1                            (d) all of these

(d) The units of 'a; are: atm litre2 mol-2

                                = atm dm6mol-2 = dyne cm2mol-2

     The units of 'b' are: litre mol-1 = dm3mol-1 = cm3mol-1

Difficulty Level:

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In the vander Waals' equation, the constant 'a' and 'b' with temperature shows which trend:

(a) both remains same

(b) 'a' remains same, 'b' varies

(c) 'a' varies, 'b' remains same

(d) both varies

(d) This is one of the limitation of vander Waal's equation.

'a' is measure of force, which is sensitive for distance, with increase in temp, the distance between molecule increase,so magnitude of force decrease. 'b' is measure of size, which is not so sensitive as 'a'   . but it also changes.

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At relatively high pressure, van der Waals' equation reduces to:

(a) PV = RT

(b) PV = RT + a/v

(c) PV = RT + Pb

(d) PV = RT - a/V2

(c) At high pressure, volume of molecules should not be neglected in comoparison to volume of gas. Also experimental to volume of gas. Also experimental studies reveals PV > RT at high P.

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When is the deviation more in the behaviour of a gas from the ideal gas equation pV=nRT?     

(a) AT high temperature and low pressure

(b) At low temperature and high pressure

(c) At high temperature and high pressure

(d) At low temperature and low pressure

(b) Gases show deviation from ideal gas behaviour when the temperature is low and pressure is high. At low temperature, the volume of one molecule is not negligible in comparison to total volume and intermolecular force of attraction is maximum at low temperature and high pressure.

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Joule-Thomson coefficient (T/P)H for an ideal gas is:

(a) zero                                  (b) +ve

(c) -ve                                    (d) none of these

(a) Ideal gas does not show Joule-Thomson effect.

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All the three states H2O, i.e., the triple point for H2O the equilibrium,

                       Ice WaterVapour exist at:

(a) 3.85 mm and 0.0981 °C

(b) 4.58 mm and 0.0098 °C

(c) 760 mm and 0°C

(d) none of the above

(b) The conditions for triple point of H2O.

 

the particular temperature and pressure at which the solid, liquid, and gaseous phases of a given substance are all at equilibrium with one another.

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The unit of van der Waals' constant 'a' is:

(a) atm litre2 mol-2                        (b) dyne cm4 mol-2

(c) newton m4 mol-2                     (d) all of these           

(d) a=P x V2 = atm litre2 mol-2 = dyne cm4 mol-2 = Newton m4 mol-2 = atm dm6 mol-2

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The unit of van der Waals' constant 'b' is :

(a) cm3 mol-1

(b) litre mol-1

(c) m3 mol-1

(d) all of these 

(d) b = 4Nv;   unit of b = litre mol-1 = cm3 mol-1 = m3 mol-1

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