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Chapter 14
Heat Transfer and Temperature Change
| Question | Answer |
|---|---|
| What are the states of matter | Solid, liquid, gas |
| State the properties of a solid | The molecules are packed closely together. It is difficult to compress a solid into a smaller volume. Large forces attract each molecule to its neighbouring molecules. The molecules have fixed positions and cannot move. This gives the solid a fixed shape. Solids do not flow. Molecules do vibrate about their fixed positions. The speed and size of the vibrations increase with temperature (usually causing the solid to expand). |
| How does a solid melt into a liquid | If sufficient heat energy is added to a solid, it reaches its melting point. Some molecules gain sufficient energy to break free from the strong forces attracting them to neighbouring molecules. These molecules become able to slide freely around each other. As more heat is added, eventually all the molecules have enough energy to do this. All of the solid has melted and has turned into a liquid. |
| State the properties of a liquid | The forces between the molecules are weaker in a liquid than in a solid. The molecules are still quite close together. A liquid is very difficult to compress into a smaller volume. The molecules can move and collide with each other. The speed varies. Liquids flow. If a molecule gets enough velocity, it can leave the surface of the liquid; this is evaporation. |
| What happens to liquid molecules during evaporation? | As further heat energy is added to the liquid, the molecules move faster. Evaporation increases, and eventually occurs throughout the liquid. This temperature is the boiling point. If energy continues to be added at this temperature, all the molecules will eventually escape. The substance turns into a gas. |
| State the properties of gases | There are large distances between the molecules, so a gas is much easier to compress. The forces between the molecules are negligible. The molecules move in random directions at high speed. The molecules collide with each other and the walls of the container. A gas expands to fill the container. |
| What happens to a substance when you add or take away heat energy? Do melting or boiling points have an effect on what happens? | If a substance is at its melting point or boiling point and is changing state, then as you add or remove heat energy, the temperature of the substance does not change. If a substance is not at its melting point or boiling point, then when you add heat energy, its temperature rises, and when you take heat energy away, its temperature falls. |
| What is the heat capacity of an object | The heat capacity of an object is the heat energy Q needed to change its temperature by 1 K (1 ⁰C). |
| What is the formula for heat | Heat = heat capacity x change in temperature Rise in temperature is directly proportional to amount of heat energy added. |
| What is the specific heat capacity of a substance | The specific heat capacity of a substance is the heat energy needed to change the temperature of 1 kilogram of that substance by 1 kelvin. |
| what is the formula for specific heat capacity | Heat energy added/lost = mass x specific heat capacity x rise/fall in temperature |
| What is latent heat | The heat energy that needs to be added or removed to change the state of a substance, without a change in temperature, is called its latent heat (L). |
| What is the specific latent heat of a substance | The specific latent heat (l) of a substance is the amount of heat energy needed to change the state of 1 kg of that substance without a change in temperature. The symbol for specific latent heat is l. The SI unit of specific latent heat is the joule per kilogram (J kg–1). |
| What is the specific latent heat of fusion of a substance | The specific latent heat of fusion of a substance is the amount of heat energy needed to change 1 kg of that substance from a solid to a liquid without a change in temperature (i.e. at its melting point). Note: The same amount of heat energy is given out when the substance changes from a liquid to a solid at its melting point. |
| What is the specific latent heat of vaporisation of a substance | The specific latent heat of vaporisation of a substance is the amount of heat energy needed to change 1 kg of that substance from a liquid to a gas without a change in temperature (i.e. at its boiling point). Note: The same amount of heat energy is given out when the substance changes from a gas to a liquid at its boiling point. |
| What is the SI unit of specific heat of vaporisation and fusion | The SI unit of specific heat of vaporisation and fusion is the joule per kilogram (J kg-1). |
| Which is larger between the specific latent heat of fusion and the specific latent heat of vaporisation | The specific latent heat of vaporisation is usually significantly larger than the specific latent heat of fusion. |
| What is a heat pump | A heat pump transfers heat energy from a cooler region to a warmer one |
| What are the three ways heat is transferred from one place to another? | Conduction Convection Radiation |
| What is conduction | Conduction is the movement of heat energy through a substance by the passing on of molecular vibration from one molecule to another. There is no overall motion of the substance. |
| What is a U-value | The U-value of a structure is the amount of heat energy conducted per second through 1 m2 of that structure when a temperature difference of 1 ⁰C (1 K) is maintained between its ends. |
| What is convection | Convection is the transfer of heat through a fluid by means of circulating currents of fluid caused by the heat. |
| What is radiation | Radiation is the transfer of heat energy from one place to another in the form of electromagnetic waves. |
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21JulianM
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