Kinetic theory (Unit 2)

Question 1

Kinetic molecular model of a:
1-Solid
2-Liquid
3-Gas

Answer 1

1-Fixed shape and volume, with high density and won’t flow.

2-Takes the shape of bottom of the container it’s in, has a fixed volume, medium density and it flows.

3-Takes up the shape and volume of the container it’s in, has a low density and it flows.

Question 2

Describe/explain Brownian Motion and give an example

Answer 2

• Brownian motion is the random jerky motion of particles viewed through a microscope.
• It’s caused by rapid collisions between moving invisible particles(molecules) and larger other particles. They collide then bounce off each other.
• E.g. dust particles in the air or pollen grains in water.

Question 3

Describe the movement of a particle in Brownian motion

Answer 3

Moves in a total long way (jerky moments) but doesn’t move far from the point in the center.

Question 4

The space and attraction between molecules in:
1-Solids
2-Liquids
3-Gases

Answer 4

1-High forces and small spaces. Fixed shape.

2-Medium forces and small spaces. Random motion.

3-Very low forces and large spaces. Random motion of molecules.

Question 5

Describe a short experiment to demonstrate evaporation

Answer 5

Put some ethanol onto the back of your hand. It feels a little cold and the ethanol evaporates off your hand. If you give it a blow it increases the rate at which the reaction occurs.

Question 6

Evaporation increases when? (3)

Answer 6

• Its warmer
• Wind is supplied
• A greater surface area

Question 7

Boyle’s law

Answer 7

• Pressure and volume are inversely proportional.
• pV = constant
• P1V1 = P2V2
• Temperature remains constant.

Question 8

What happens to the molecules when they expand due to heat and what is this process called?

Answer 8

• Thermal expansion

- The molecules move/(vibrate if it’s a solid) faster so the gaps between the molecules increase.

Question 9

When thermal expansion occurs.

Order the 3 states into the order of how much they expand. (Lowest to highest)

Answer 9

• Solid
• Liquid
• Gas

Question 10

Uses of thermal expansion? (2)

Answer 10

• Thermometers

- Thermostats

Question 11

What is a thermostat? Describe the experiment.

Answer 11

Take a bimetallic strip and hold it above a flame from a bunsen burner. The strip will bend away from the flame. This is because the molecules at the bottom of the bimetallic strip (that’s closest to the flame) expands.

Question 12

Disadvantages of thermal expansion? (3)

Answer 12

• Bridges (don’t want them to expand)
• Power lines (can break)
• Freezing pipes (can burst)

Question 13

• What are fixed points?

- Fixed points of water?

Answer 13

• The freezing and boiling point of a substance

- 0 degree C and 100 degree C

Question 14

Define sensitivity

Answer 14

The expansion (or change) per degree celcius

Question 15

Define linearity

Answer 15

The same expansion (or change) per degree celcius

Question 16

What does the range of a thermometer depend on?

Answer 16

The boiling point and freezing points of the liquid or other properties as well.

Question 17

What apparatus is used to measure temperature difference between 2 different metals?

Answer 17

Thermocouple

Question 18

Describe the wires of a thermocouple and give examples of each

Answer 18

• There are 3 wires.
• Wires 1 and 2 are made of the same material e.g. copper
• Wire 3 is different to wires 1 and 2 e.g. constantan

You can’t have 2 wires made of very conductive metals or both that are made of very conductive metals.

You would have one of each.

Question 19

What must the junction have on a thermocouple?

Answer 19

2 different wires meeting at the junction

Question 20

How do the wires cause a voltage in a thermocouple?

Examples of meters that are used to measure the voltage produced. (4)

Answer 20

The two different wires joined together, at the same temperature will cause a voltage. This is read on a meter such as:

• Galvanometer
• Millivoltmeter
• Milliammeter
• Digital voltmeter or ammeter

Question 21

In a thermocouple what is commonly done with the cold junction?

Answer 21

It’s put into ice. This is so we can compare the temperature to a known valur (0 degree C)

Question 22

Advantages of a thermocouple? (6)

Answer 22

• Rapid response to change in temperature
• Small thermal capacity - doesn’t affect the measurement
• Can be used as a data logger for continuous measurement
• Can measure a large range
• Has a small area
• Can be used for remote readings if connected via the internet to a PC and the internet

Question 23

What is the internal energy?

Answer 23

The internal energy is the sum of all the KE and PE energies of its atoms/ molecules

Question 24

How do you increase the internal energy? (2)

Answer 24

• Supply more thermal energy

- Doing work on the system e.g. compressing it

Question 25

Define heat capacity

Answer 25

Heat capacity is the amount of energy required to raise the temperature of a body by 1K or 1 degree C

Question 26

Define specific heat capacity

Answer 26

Specific heat capacity is the amount of energy required to raise 1Kg (unit mass) of a substance by 1K or 1 degree C

Question 27

Specific heat capacity = ? | Include units and symbols

Answer 27

specific heat capacity = energy supplied / (mass * delta feta(or temperature)) C = Q / (m*delta T) Specific heat capacity = C (J/kg/degree C) Energy supplied = Q (J) Change in temperature = delta T(or feta) (degree C)

Question 28

1-What is latent heat of fusion? 2-What is latent heat of vaporisation?

Answer 28

1-Solid to a liquid vice-versa 2-Liquid to gas vice-versa

Question 29

Define specific latent heat

Answer 29

Specific latent heat is the energy needed per Kg of a substance to change the state

Question 30

Specific latent heat of fusion = ? | Include units and symbols

Answer 30

Specific latent heat of fusion = energy supplied / mass of substance melted L = Q / M ``` L = specific latent heat (J/Kg) Q = energy supplied (J) M = mass (kg) ``` Remember to use the E = Pt or E = VIt if Q is not directly given to you. If you use g for mass then change the unit for L to J/g

Question 31

Specific latent heat of vaporisation = ? | Include units and symbols

Answer 31

Specific latent heat of vaporisation = energy supplied / mass of substance vaporised L = Q / M ``` L = specific latent heat of vaporisation (J/kg) Q = energy supplied (J) M = mass (kg) ``` Remember to use the E = Pt or E = VIt if Q is not directly given to you. If you use g for mass then change the unit for L to J/g

Question 32

Rules for latent heat? (2)

Answer 32

- Energy is supplied to melt or boil a substance | - Energy is given out on freezing or condensation

Question 33

4 methods of heat transfer and what they can happen in

Answer 33

- Conduction = mainly solids - Convection = fluids - Radiation = doesn't require a medium so it can happen in a vacuum - Evaporation

Question 34

Thermal radiation is the same as what?

Answer 34

Infrared radiation which is an EM wave

Question 35

1-What objects are better are absorbing and emitting radiation? 2-What objects are worse at absorbing and emitting radiation? Why?

Answer 35

1-Dull and dark objects 2-Shiny and light objects. Shiny objects reflect light.

Question 36

Ways to insulate a house? (5)

Answer 36

- Double glazing - Cavity wall insulation - Loft insulation - Insulate hot water tank - so you don't waste heat - Turn down the radiators