STATES OF MATTER CLASS 11

CHAPTER 5 STATES OF MATTER

1. What is an ideal gas? Write its characteristics.

An ideal gas is a hypothetical gas that obeys the ideal gas equation PV = nRT under all conditions.
Characteristics:

• No intermolecular forces.

• Molecular volume is negligible.

• Collisions are perfectly elastic.

• Obeys Boyle’s, Charles’s and Avogadro’s laws.

2. State Boyle’s Law.

At constant temperature, the volume of a fixed mass of a gas is inversely proportional to its pressure.
PV = constant.

3. State Charles’s Law.

At constant pressure, the volume of a gas is directly proportional to its absolute temperature.
V/T = constant.

4. What is Avogadro’s Law?

Equal volumes of all gases under the same temperature and pressure contain equal number of molecules.
V ∝ n

5. Define Dalton’s Law of Partial Pressures.

Total pressure exerted by a mixture of non-reactive gases is equal to the sum of partial pressures of individual gases.
P_total = P1 + P2 + P3 + …

6. What is vapour pressure?

The pressure exerted by vapours in equilibrium with their liquid (or solid) at a given temperature is called vapour pressure.

7. State Graham’s Law of Diffusion.

Rate of diffusion of a gas is inversely proportional to the square root of its molar mass.
r ∝ 1/√M

8. Derive the ideal gas equation from gas laws.

From Boyle’s Law: V ∝ 1/P
From Charles’s Law: V ∝ T
From Avogadro’s Law: V ∝ n
Combining:
V ∝ nT/P
⇒ PV = nRT

9. What are intermolecular forces?Name their types.

Intermolecular forces are forces of attraction between molecules.
Types:

1. Dipole–dipole forces

2. Dipole–induced dipole forces

3. London dispersion forces

4. Hydrogen bonding

10. What is compressibility factor (Z)?

Z = PV / nRT
For an ideal gas, Z = 1.
Z < 1 → more compressible
Z > 1 → less compressible

11. When do real gases show ideal behaviour?

Real gases behave ideally under:

• High temperature

• Low pressure

• Negligible intermolecular forces

12. Write van der Waals equation for real gases.

(P + a/V²)(V – b) = RT
where:
a = measure of attraction
b = effective molecular volume

13. Write two postulates of kinetic molecular theory of gases.

• Gas molecules are in constant random motion.

• Intermolecular forces are negligible.

• Pressure arises due to collisions with container walls.

• Average kinetic energy is directly proportional to absolute temperature.

(Any two can be written.)

14. What is RMS velocity? Write the formula.

Root Mean Square velocity is the square root of the mean of squares of molecular velocities.
u_rms = √(3RT / M)

15. What is liquefaction of gases?

Conversion of a gas into liquid is called liquefaction.
Conditions:

• High pressure

• Low temperature

• Strong intermolecular forces