Gaseous - Liquid - Solid States- Multiple Choice Questions

1. Helium atom is two times heavier than a hydrogen molecule. At 298 K, the average kinetic energy of a helium atom is

a. same as that of a hydrogen molecule
b. two times that of a hydrogen molecule
c. four times that of a hydrogen molecule
d. half that of a hydrogen molecule
(JEE 1982)

Answer: (a)

2. among the following, the molecule that is linear is

a. CO2
b. NO2
c. SO2
d. ClO2
(JEE 1982)

ans : (a)

CO2 is a linear molecule

3. A liquid is in equilibrium with its vapour at its boiling point. On average, the molecules in the two phases have equal:

a. inter-molecular forces
b. potential energy
c. kinetic energy
d. temperature
(JEE 1984)

Answer (d)

4. Rate of diffusion of a gas is:

a. directly proportional to its density
b. directly proportional t its molecular weight
c. directly proportional to the square root of its molecular weight
d. indirectly proportional to the square root of its molecular weight
(JEE 1985)

Answer (d)

5. the average velocity of an ideal gas molecule at 27°C is 0.3 m/s. the average speed at 927°C will be:

a. 0.6 m/s
b. 0.3 m/s
c. 0.9 m/s
d. 3.0 m/s
(JEE 1986)

Answer: (a)

Gaseous, Liquid, Solid State - True or False Type Questions

1. When a liquid and its vapour are in equilibrium and the pressure is suddenly decreased, cooling occurs. (JEE 1984)

True

Reason: The decrease in pressure results in further evaporation of the liquid into gaseous phase. The energy required for this is realized from the liquid itself which causes a decrease in temperature.

2. Kinetic energy of molecules is zero at 0°C. (JEE 1985)

Ans: False

The equation relating energy of molecules to temperature is in absolute temperature and not centigrade temperature.

3. A gas in a closed container will exert much higher pressure due to gravity at the bottom than at the top. (JEE 1985)

False.

It is equal in all directions.

4. Heat capacity of a diatomic gas is higher than that of a monatomic gas. (JEE 1985)
True

Diatomic gas has translational, rotational, and vibrational energies. Monatomic gas has only translational energy.

5. In the van der Waals equation,

[p + n²a/V²][V-nb] = nRT

the constant ‘a’ reflects the actual volume of the gas molecules.

False

Reason: In the equation ‘a’ is a measure of the forces of attraction between gaseous molecules and b is a measure of effective volume occupied the molecules of 1 mol of a gas.

Solid, Liquid, Gas Phases - 21 - Fill Blanks Type

1. Cp – Cv for an ideal gas is ____________.
(JEE 1984)

Answer : R
(See page No. 67 H C Verma part 2)

2. The rate of diffusion of gas is ______________________ proportional to the square root of molecular mass.
(JEE 1986)

Answer: inversely
(Graham’s law of diffusion: The rate of diffusion of a gas is inversely proportional to the square root of its density or molar mass.)

3. The value of PV for 5.6 litres of an ideal gas is _________________ RT at STP.
(JEE 1987)

Answer: ¼ or 0.25
1 mole of an ideal gas at STP has a volume of 22.4 litres

4. Eight grams of oxygen and hydrogen at 27°C will have the total kinetic energy in the ratio of __________________.
(JEE 1989)

Answer: 1:16

Reason: For a mixture of gases, in thermal equilibrium, average kinetic energy of all molecules is same.

(½)*m1* v1² = (1/2)*(m2*v2²

Oxygen’s molecular weight is 32 and hence 8 grams will have 8/32 = ¼ moles.
Hydrogen’s molecular weight is 2 and hence 8 grams will have 8/2 = 4 mols

Total kinetic energy of oxygen moleculues = (¼ )* (½)*m1* v1²
Total kinetic energy of hydrogen molecules = 4*(1/2)*(m2*v2²

The ratio will be (1/4)/4 = 1/16 as remaining terms or equal in both cases.

5. The shape of [CH3] ⁺ is ___________________.
(JEE 1990)

Answer: Planar

6. Among N₂0, S0₂, I₃3⁺, I₃^-, the linear species are ____________ and __________ .
(JEE 1997).

Answer: N₂0, I₃3^-

7. A liquid which is permanently supercooled is frequently called as ___________.
(JEE 1997)

Answer: glass