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.