Chapter 9 - Kinetic Model of Matter

The kinetic model of matter states that

• atoms and molecules move in continuous and non-random motion.

• atoms and molecules move in continuous and random motion.

• the kinetic energies of atoms and molecules increase with increasing temperature.

• the pressure of atoms and molecules is due to the collision of these particles with

  the walls of the container they are in.

Using a microscope, Peter observes that some pollen grains suspended in water move in an irregular manner. This is due to the

• pollen grains colliding with one another.

• pollen grains repelling one another.

• bombardment of pollen grains by water molecules.

• bombardment of water molecules by pollen grains.

Choose the most appropriate phrase to complete the following statement.

 

As the temperature of a gas increases, the gas molecules

• gain kinetic energy and move faster.

• occupy a smaller volume with pressure remaining constant.

• exert a lower pressure with volume remaining constant.

• occupy the same volume with pressure remaining constant.

A diver deep underwater exhales an air bubble. The air bubble is observed to increase in size as it rises to the surface. Which of the following explanations may be used to describe this phenomenon?

 

1. The volume increases because the pressure underwater decreases with decreasing depth.

2. The volume increases because while the pressure underwater remains the same, the temperature of the water is lower (i.e. colder) with greater depth.

3. The volume increases because while there is no pressure underwater, there is atmospheric pressure at the surface of the water.

• 1 only

• 2 only

• 1 and 3 only

• 2 and 3 only

Predict (with the appropriate explanation) what will happen to the volume of a helium-filled balloon after it is released into the air.

• Its volume increases because it is warmer in the upper atmosphere.

• Its volume increases because it needs to be less dense in order to continue rising.

• Its volume increases because the atmospheric pressure is lower in the upper atmosphere.

• Its volume decreases because the pressure in the balloon increases with increasing

  altitude (height above the ground).

Siti pumps air into her bicycle tyre using a hand pump. After a few pumps, she feels the tyre getting warmer. Which of the following statements explain(s) this phenomenon?

 

1. The number of air molecules increases, and thus the frequency of collisions of the air molecules with the tyre walls increases. This results in the higher temperature of the air in the tyre.

2. The tyre expands, which increases the distance between the inner walls of the tyre. This results in the higher temperature of the air in the tyre.

3. The pressure in the tyre is lower as more air is introduced into the tyre. With a lower pressure in a constant-volume container (tyre), the temperature increases.

• 1 only

• 1 and 2 only

• 2 and 3 only

• 3 only

Bala compresses the air trapped in a gas syringe slowly at constant temperature. As he does so, the pressure in the gas syringe increases. This is because the

• air molecules gain kinetic energy as a result of this compression.

• air molecules now move even more continuously and randomly.

• air molecules collide with the walls of the syringe more frequently.

• air molecules gain thermal energy as a result of this compression.

Some air is trapped in a syringe by a movable piston. The initial volume of the trapped air is 0.25 m³ at a pressure of 800 mm Hg. The piston is pulled outwards such that the volume of air increases to 0.50 m³. Assuming that no air escapes or enters the syringe, and that the temperature inside the syringe remains constant, what is the new pressure inside the syringe?

• 400 mm Hg

• 760 mm Hg

• 800 mm Hg

• 1600 mm Hg

A balloon filled with air is cooled with liquid nitrogen to very low temperatures. This causes the balloon to decrease in volume significantly. Choose the statement that explains this phenomenon most accurately.

• The air molecules move with higher speeds, so the volume of the balloon

  decreases.

• The air molecules have lower kinetic energies and this can be related to a

  decrease in the mass of the air molecules. With a smaller mass, the volume decreases.

• The air molecules contract at the low temperatures. This causes the sizes of the

  air molecules to become smaller. This results in a smaller volume.

• The pressure in the balloon becomes lower. The atmospheric pressure around the balloon compresses the balloon, causing its volume to decrease.

We can increase the pressure of a gas in an enclosed container by

• increasing its volume and increasing its temperature.

• increasing its volume and decreasing its temperature.

• decreasing its volume and decreasing its temperature.

• decreasing its volume and increasing its temperature.