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CHAPTER 2 • 8 MARKS

Behaviour of Gases

Understand Boyle’s law, Charles’s law, absolute temperature, ideal gas behaviour and gas-law numericals.

Topics in this chapter

  1. Pressure and volume of a gas
  2. Boyle’s law
  3. Temperature and volume of a gas
  4. Charles’s law
  5. Absolute zero and Kelvin scale
  6. Combined gas law
  7. Ideal gas equation
  8. Numerical problem solving

Key learning points

✓ At constant temperature, pressure is inversely proportional to volume.

✓ At constant pressure, volume is directly proportional to absolute temperature.

✓ Kelvin temperature equals Celsius temperature plus 273 approximately.

✓ Gas-law calculations require consistent units.

Important equations and relations

P₁V₁ = P₂V₂V₁/T₁ = V₂/T₂P₁V₁/T₁ = P₂V₂/T₂PV = nRT

Multiple-choice questions

1. At constant temperature, if gas volume is halved, pressure becomes:
  1. Half
  2. Double
  3. Four times
  4. Unchanged

Answer: B — Double

2. 0°C is approximately equal to:
  1. 0 K
  2. 100 K
  3. 273 K
  4. 373 K

Answer: C — 273 K

3. The ideal gas equation is:
  1. PV = nRT
  2. P/T = nV
  3. V = PR
  4. PT = nR/V

Answer: A — PV = nRT

Very short-answer questions

  1. State Boyle’s law.
  2. Convert 27°C to kelvin.
  3. What is absolute zero?

Short-answer questions

  1. Explain Charles’s law with a suitable graph description.
  2. A gas occupies 2 L at 1 atm. Find its volume at 2 atm at constant temperature.

Long-answer question

  1. Derive and explain the combined gas law and show how Boyle’s and Charles’s laws follow from it.