Name:______________________ Class:_________________ Teacher:____________________

KS3 Heating and Cooling Topic BookletThermal energy and particle theory

Big Picture

Thermal energy

Thermal (or heat) energy is a form of energy everything above -273oC (0 K) has and is sometimes called internal energy. A measure of thermal energy is temperature and when we change the temperature of substances their states can change. These states are solid, liquid and gas (there is a fourth state called plasma, but you will come to that later in school/university).

1. Draw the representations of the three states of matter below

Solid Liquid Gas

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2. Using your diagrams above how the particles are arranged in:a) Solid

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b) Liquid

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c) Gas

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When you increase the thermal energy in a substance, by heating it up and increasing the temperature, the particles begin to move more and more. As particles heat up, they begin to more around more and more. When they move enough, they are able to change state. As particles cool down, they move around less and less

The temperature at which the particles have enough energy to move further apart and change state has a specific name depending on the state changing from and too. These are shown in the diagram below.

3. Identify and describe the following state transitionsa) Solid to Liquid

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b) Solid to gas

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c) Liquid to gas

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d) Liquid to solid

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e) Gas to liquid

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f) Gas to solid

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Temperature is measure using a thermometer and we can use temperature, along with the mass and specific heat capacity (c) of a material to calculate the amount of thermal energy transferred. This is used in chemistry and physics all the way to university and is very important in comparing fuels of the future.

4. When is temperature useful?

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5. Can you think of an example when temperatures are used?

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6. What has temperature got to do with particles movements?

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7. Why do objects heat up?

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8. Ext: Why do some objects heat up faster than others?

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Conduction

Conduction is the way that thermal energy is travels through solids and liquids, and to a much lesser extent in gases. Conduction requires particles (atoms and molecules) to be in contact and the thermal energy is transferred by these particles colliding.

Heat is transferred through solids by conduction. The particles are always vibrating and when they get hotter; they have more energy and so

vibrate more (this is an increase in kinetic energy of the particles). When you heat one end up of a metal up, the particles begin to vibrate more, colliding with

neighbouring particles causing them to vibrate more and the thermal energy is transferred.

9. How could we model conduction? Do a diagram below of a model for conduction in a solid.

10. How do the particles in a solid or liquid behave if they are heated?

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Direction of energy travel

11. Does the heat or the cold spread? Why?

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12. Explain how is heat transferred through the object?

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Conduction occurs through some substances more quickly than others. This is because in all substances there are tiny forces holding them together. In some objects, the force holding the together is very weak, and in others it can be quite strong. In metals, free electrons move around easily and allow heat to be conducted (passed) through the metal very quickly. This makes metals good thermal conductors. In plastics, the particles are held together by very strong forces and therefore it is more difficult for the particles to vibrate. This means the thermal energy is less able to move plastics and these are poor thermal conductors, often called insulators. Gas substances are poor conductors of thermal energy as their particles are too far away from each other and are less likely to collide and transfer the energy by conduction.

13. Why do some substances conduct heat better than others?

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14. Suggest some good conductors and explain why they are good

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15. Suggest some poor conductors (insulators) and explain why they are poor

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16. If you were design a saucepan, what would you make the main body out of? Why?

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17. If you were designing a saucepan, what would you make the handle out of?

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18. Are gases good conductors of thermal energy? Why?

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19. Complete the following sentences

a) Wool is a good insulator because_________________________________________________________________________________________________________

b) Wool is a good insulator but_____________________________________________________________________________________________________________

c) Wool is a good insulator so ______________________________________________________________________________________________________________

Convection

In liquids and gases, where particles are able to move more, thermal energy can also be transferred via convection. Convection is a process that causes hotter particles rise and cooler particles to fall based on their density.

Density is a measure of the number of particles (sometimes measured in grams) in a volume of the substance (sometime a cm3). So, when particles move more, they occupy a larger volume and therefore their density decreases.

As particles increase their thermal energy, they move more and become less dense. This causes them to rise. As particles begin to cool and decrease their thermal energy, they move less and become more dense. This causes them to drop. This create flow, or current, known as a convection current and can be observed in many different situations.

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Highest density (most particles in volume

Lowest density (least particles in volume

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Another example is heating water in a saucepan.

20. Explain what is happening in this diagram

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21. In the day, the land at the coast is warmer than the see so particles in the air are warmer above the land then the sea. Draw a diagram below to show the convection current of air at the sea during the day.

22. In the evening, the sea retains its heat better (it has a high specific capacity for heat) and therefore the sea is warmer than the land. Explain how your diagram above would change in for the coast at night.

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23. In your own words, what is density?

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24. In your own words, how does density change a particles heat up (increase thermal energy)?

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25. In your own words, how do convection currents occur?

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26. Where else might convection currents occur?

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Radiation

If space is a vacuum (no particles), how do we feel the suns heat? This is a very good questions as the two ways thermal energy can travel have both involved particles. Radiation does not involve particles, instead it uses waves, such as light and infrared waves, to carry the energy to earth. Another example of radiation is how you feel the warmth of fire when stood beside it.

27. How do we feel the thermal energy from the sun if there are no particles in space?

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28. How is thermal radiation transferred?

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Different colours also absorb (take in) and emit (release) thermal radiation at different rates. White absorbs and emits only a little amount of thermal radiation, whereas black absorbs and emits much more. This can be seen in a Leslie Cube (see below)., where hot water is put in the middle and the darker side of the cube raises to a higher temperature then the lighter side. This is because the black absorbs and emits more thermal energy.

29. How can the Efficiency of a Radiator be Improved? Think about colour.

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30. Will an Object Emit Radiation Faster with a Matt or a Shiny Surface?

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31. Will an Object Emit Radiation Faster with a Dark or a Light Surface?

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32. Why is part of the Space Shuttle covered in Matt Black Tiles?

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Review questions

33. Draw a particle diagram for a solid, liquid and gas

34. Describe the effect an increase in temperature has on the particles of a substance

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35. How does heat travel via conduction?

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36. How does heat travel via convection?

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37. How does heat travel via radiation?

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38. Give some examples of thermal conductors

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39. Why are these good conductors?

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40. Give some example of thermal insulators

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41. Why are these good insulators?

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42. Think. Can you let the cold in?

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43. Label and explain all the forms of thermal energy transfer taking place in the picture below.

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Interleaved and recall questions

44. What unit is Energy measured in?__________________________________________________________________________

45. Name three Forms of Energy.__________________________________________________________________________

46. What does "Energy is Transferred" mean?__________________________________________________________________________

47. What is the Conservation of Energy?

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48. What unit is Temperature measured in?

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49. What is Temperature a measure of?

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50. Can Heat be Transferred by Conduction in a Solid? Why?

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51. Can Heat be Transferred by Conduction in a Liquid? Why?

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52. Describe the Conduction of Heat in Non-metals.

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53. Is the Conduction of Heat in Non-metals Fast?

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54. Is the Conduction of Heat in Metals Fast?

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55. Can Heat be Transferred by Convection in a Liquid?

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56. Can Heat be Transferred by Convection in a Gas?

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57. Describe how Heat can be Transferred by Convection.

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58. What are Convection Currents caused by?

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59. Describe how a Radiator can Heat a Room in a House.

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60. What does a Heat Insulator do?

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61. Name two Materials which could be used as Insulators.

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62. How does the Fur of Animals keep them Warm?

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63. How can Air Transfer Heat across the Gap in Cavity Walls?

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64. What Material can be used to fill the Gap in Cavity Walls to keep your house warm?

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65. Does Draught Proofing Reduce Heat Loss by Conduction or Convection?

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66. How can Heat Loss by Radiation or Reduced?

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