P.3.6.2.3 Molecular Kinetic Theory Model

Brownian motion

• makes it possible to see the motion of air molecules.

• is caused by the collisions of smoke particles.

• is caused by collisions between air molecules and smoke particles.

• occurs because air is a mixture of gases and the molecules have different masses.

Which is not an assumption about gas particles in the kinetic theory model for a gas?

• They collide elastically with the container walls.

• They have negligible size compared to the distance between the container walls.

• They travel between the container walls in negligibly short times.

• They collide with the container walls in negligibly short times.

The average mass of an air molecule is 4.8 × 10^–26 kg

What is the mean square speed of an air molecule at 750 K?

• 3.3 × 10⁵ m² s^–2

• 4.3 × 10⁵ m² s^–2

• 6.5 × 10⁵ m² s^–2

• 8.7 × 10⁵ m² s^–2

A transparent illuminated box contains small smoke particles and air. The smoke particles are observed to move randomly when viewed through a microscope.

What is the cause of this observation of Brownian motion?

• Smoke particles gaining kinetic energy by the absorption of light.

• Collisions between smoke particles and air molecules.

• Smoke particles moving in convection currents caused by the air being heated by the light.

• The smoke particles moving randomly due to their temperature.

The diagram shows a gas particle about to collide elastically with a wall.

Which diagram shows the correct change in momentum Δmv that occurs during the collision?

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The composition of a carbon dioxide (CO₂) molecule is one atom of ¹²₆C and two atoms of ¹⁶₈O.

What is the number of molecules of CO₂ in 2.2 kg of the gas?

• 1.0 × 10²²

• 3.0 × 10²²

• 3.0 × 10²⁵

• 4.7 × 10²⁵

What is the total internal energy of 2.4 mol of an ideal gas which has a temperature of 15 °C?

• 6.0 × 10^–21 J

• 1.4 × 10^–20 J

• 4.5 × 10² J

• 8.6 × 10³ J

Which of the following is not used as valid assumption when deriving the equation P =  (1/3) Nm (crms)2 in the simple kinetic theory of gases?

• The molecules suffer negligible change of momentum on collision with the walls of the container.

• Attractive forces between molecules are negligible.

• The duration of a collision is negligible compared with the time between collisions.

• The volume of the molecules is negligible compared with the volume of the gas.

A fixed mass of gas occupies a volume V. The temperature of the gas increases so that the root mean square velocity of the gas molecules is doubled.

What will the new volume be if the pressure remains constant?

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• 2V

• 4V

Which one of the following is not an assumption about the properties of particles in the simple kinetic theory?

• < c² > is the average speed of the particles

• The forces between the particles are negligible except when particles collide

• The time spent by particles in collision is negligible compared with the time spent between collisions

• The volume of the particles is negligible compared to the volume of the container