Chapter 9: The Kinetic Theory Particle

Question 1

Why do particles in a solid or liquid stick together? (2)

Answer 1

-It is due to the attractive forces (forces pulling
them together and holding the particle in a fixed place in solids) between them.
-It is also due to the bonds between the particles. The bonds are strongest in solids due to the particles being closer together, solids are rigid.

Question 2

Why do particles in gases not stick together? (2)

Answer 2

-Due to the particles in gas being farther apart compared to a solid or a liquid,
- there are no attractive forces between the particles and no bonds as they are not close enough together

Question 3

Brownian Motion

Answer 3

The random movement of heavier particles
(suspended in a liquid or gas) due to the molecular bombardment by the fast-moving but lighter particles is called Brownian Motion.

Question 4

Why are collisions elastic?

Answer 4

All collisions are elastic meaning that they do not lose kinetic energy as they bounce off each other.

Question 5

Describe how air molecules cause the smoke particles to follow the observed path. (zigzag) (4)

Answer 5

-Although smoke particles are many times heavier than air particles, as they are light
-The air particle moves with greater average kinetic energy and collides with the smoke particle.
-As they collide, it is enough impact to change the direction of the smoke particle.
-The more collisions the more random the movement of the smoke particles is.

Question 6

Describe what is seen in the microscope focused on the smoke particle. (3)

Answer 6

-Smoke particles are seen moving randomly,
-They are in constant motion due to their average kinetic energy,
-They are moving in all directions and in a zigzag manner.

Question 7

Describe what is seen as the smoke particles move towards and away from the observer- (4)

Answer 7

-Smoke particles are constantly bombarded by the lighter but faster air particles that are in motion due to their average kinetic energy.
-Hence causing them to move in straight lines in all directions randomly.
-They move in and out of focus or disappear.
-They may also appear dimmer or brighter depending on how close they are to the observer.

Question 8

Why does a gas cause pressure on the walls of its container? (4)

Answer 8

-As the particles in a gas move constantly and at random with the highest average kinetic energy, they collide with one
another a lot.
-When compressed or contained in a closed space, the particles still move with the same average speed (and randomly) but their motion is limited.
-As they move quickly, this causes more particles to constantly collide with the walls of the container.
-The more they collide with the walls (in a particular area), the more force they exert due to the changing momentum, and the more pressure is caused.

Question 9

What happens to a gas when heated? (4)

Answer 9

-As temperature increases by heating
-The average kinetic energy of the gas
particles increase hence they move faster,
(…and how does it impact pressure?)
-Causing more collisions to occur with the walls of the container,
-Increasing the force exerted (at particular areas) due to changing momentum, thus increasing the pressure.

Question 10

What happens to a gas when cooled? (4)

Answer 10

-As temperature decreases by cooling
-The average kinetic energy of the gas particles decreases hence they move slower,
(…and how does it impact pressure?)
-Causing fewer collisions to occur with the
walls of the container,
-Decreasing the force exerted (at particular areas) due to changing momentum, thus decreasing the pressure.

Question 11

What happens to a gas when it is compressed? (4)

Answer 11

-Decreasing the volume of a gas,
-This causes them to not move as far between
collisions due to the smaller space,
(…and how does it impact pressure?)
-And hence collide with the walls more often,
-Increasing the force exerted (in particular areas) due to changing momentum, thus increasing the Pressure.

Question 12

Why do thermometers take time to measure
the temperature?

Answer 12

Thermal energy has to either be transferred to or from the thermometer until it is at the same
temperature as the thing it is measuring.

Question 13

How to create a thermometer- (4)

Answer 13

-Put the thermometer in melting ice
and mark 0 degrees.
-Put the thermometer in boiling water and mark it 100 degrees.
-Divide the space between the 2 measurements into 100 parts.
-Each part represents 1 degree.

Question 14

The Celsius scale has 2 fixed points- (2)

Answer 14

-0 degrees: the melting point of pure ice at atmospheric pressure.
-100 degrees: the boiling point of pure water
at atmospheric pressure.

Question 15

Boyle Law

Answer 15

The volume of a fixed mass of gas is inversely proportional to its pressure, provided its temperature remains constant.

Question 16

Charles Law

Answer 16

For a fixed mass of gas, The volume of a gas is directly proportional to absolute temperature, provided the pressure is constant.

Question 17

Gay Lussac’s Law

Answer 17

For a fixed mass of gas, the temperature is directly proportional to pressure, provided at volume is constant.

Question 18

Explain the observations in terms of
pressure and the volume of the gas in the cylinder (3)

Answer 18

-The pressure of the gas decreases, and the volume increases
-Initially, there is larger pressure inside than outside.
-It stops moving when the inside pressure equals the outside pressure

Question 19

When temperature increases, explain what happens to the pressure of the gas inside the
cylinder in terms of molecules when heat is applied. (4)

Answer 19

-As temperature increases, pressure also increases
-The average speed of the molecules increases or their momentum increases,
-Molecules collide with the walls more frequently
-The molecules exert a greater force on the walls due to the greater change in momentum thereby increasing the pressure.

Question 20

In terms of the momentum of molecules, how does that gain in the balloon exert pressure? (3)

Answer 20

-There is a change in the momentum of molecules during collisions,
-The molecules collide with the walls with greater average kinetic energy
-Hence increasing the momentum.

Question 21

Explain, in terms of energy, the process which takes place as a solid at its melting point
changes into a liquid at the same temperature.

Answer 21

energy / work / thermal energy / (latent) heat required
AND
to break bonds (between molecules) / to overcome attractive forces
(between the molecules) / to increase the potential energy of the molecules