Understanding the Behavior of Air in a Sealed Container
📘 Question:
An empty sealed container contains air. Which statements describe the behaviour of air particles in the container?
- I. The particles are held by very weak forces of attraction.
- II. The particles are evenly spaced and far apart.
- III. The particles are in constant and random motion.
- IV. More particles will be found at the bottom after some time.
Options:
- A) I and I
- B) I and II
- C) I, II and III
- D) I and III
✅ Statement I: “The particles are held by very weak forces of attraction”
This is true. According to the kinetic theory of gases, gas molecules are assumed to experience either no intermolecular forces or only very weak ones. Real gases do have weak van der Waals forces, but these are negligible at room temperature due to the high kinetic energy of the particles.
❌ Statement II: “The particles are evenly spaced and far apart”
This is false as written. While gas particles are indeed far apart on average, they are not evenly spaced. They move in constant random motion, and their spacing varies continuously and unpredictably over time.
✅ Statement III: “The particles are in constant and random motion”
This is completely true and one of the core postulates of the kinetic theory of gases. Particles in a gas are always moving randomly and in all directions, colliding with each other and the walls of the container.
❌ Statement IV: “More particles will be found at the bottom after some time”
This is false. In a sealed container at equilibrium, particles are uniformly distributed throughout the container. The effect of gravity is negligible compared to the thermal motion of gas particles, so there is no significant settling of particles at the bottom.
✔️ These statements best describe the behavior of air particles in a sealed container according to the kinetic theory of gases.