Behaviour of Gases
“The behavior of gases is governed by fundamental laws which relate pressure, volume, temperature, and number of gas particles.”
Characteristics of Gases
- Gases have neither fixed shape nor fixed volume.
- They are highly compressible and expand to fill the container.
- Gas particles move rapidly and randomly in all directions.
Important Gas Laws
Boyle’s Law
At constant temperature, the pressure of a gas is inversely proportional to its volume.
Formula: P × V = constant
Charles’ Law
At constant pressure, the volume of a gas is directly proportional to its absolute temperature.
Formula: V/T = constant
Avogadro’s Law
Equal volumes of all gases under the same conditions of temperature and pressure contain an equal number of molecules.
1 mole of gas = 22.4 L at STP
Ideal Gas Equation
The ideal gas law combines Boyle’s, Charles’, and Avogadro’s laws:
PV = nRT
- P = pressure
- V = volume
- n = number of moles
- R = gas constant (8.314 J/mol·K)
- T = temperature in Kelvin
Deviation from Ideal Gas
Real gases deviate from ideal behavior under high pressure and low temperature.
- Real Gas: Intermolecular forces exist
- Ideal Gas: No intermolecular forces
Van der Waals Equation: \[(P + a/V²)(V - b) = RT\]
Applications of Gas Laws
- Understanding air pressure and weather patterns
- Design of syringes and gas cylinders
- Breathing mechanisms in the human body
Previous Year Questions
- SSC JE 2021: Which law states that volume is inversely proportional to pressure at constant temperature?
- Boyle’s Law
- RRB NTPC 2019: What is the value of the gas constant R?
- 8.314 J/mol·K
- HSSC 2020: What is the volume occupied by 1 mole of gas at STP?
- 22.4 liters
Did You Know? The airbags in vehicles inflate using rapid chemical reactions that release nitrogen gas instantly!
Conclusion
The behavior of gases is predictable under ideal conditions and helps us understand a wide range of phenomena from weather to respiration. Mastery of gas laws is essential for further studies in physics, chemistry, and engineering.