P1a (ii) Heating Houses

1. www.PhysicsGCSE.co.uk P1a (ii) Heating Houses You will learn about: Factors that affect the amount of energy needed to change the temperature of a substance (Specific Heat Capacity) Factors that affect the amount of energy needed to change the state of a substance (Specific Latent Heat)

2. www.PhysicsGCSE.co.uk Heating a substance For a substance to be heated to a particular temperature three considerations are needed to determine the amount of energy required: • How much liquid there is in the beaker • What the liquid is • The rise of temperature required More liquid requires more energy Dependent on Specific Heat Capacity Higher temperature rise means more energy needed

3. www.PhysicsGCSE.co.uk Changes of State When a solid is heated, its temperature rises until it changes into a liquid. If the liquid is heated eventually the liquid will turn into a gas. The inclines represent the state of matter (Solid, Liquid or Gas). When heat energy is added the temperature rises over a period of time. The plateaus represent where the substance is changing state. There is no temperature rise even though heat energy is being applied! Gas Liquid Solid Temperature (°C) Change of State: Liquid to a Gas Time (seconds) Change of State: Solid to a Liquid

4. www.PhysicsGCSE.co.uk Change of State explained This means that a substance that is heated will continue to rise in temperature. The thermal energy transfers into kinetic energy and the molecules of the substance vibrate more and more. Represented by inclines Specific Heat Capacity: The amount of energy needed to change the temperature of one kilogram of a substance by one degree Celsius. The unit is (J/kg °C) This means that sometimes when a substance is heated it will not rise in temperature. Instead of rising in temperature the energy is used to break the bonds holding the molecules together. Specific Latent Heat: The amount of energy needed to change the state of one kilogram of a substance without a change in temperature. The unit is (J/kg) Represented by plateaus Energy cannot do two things at the same time! It cannot raise the temperature AND break the bonds of a substance. If it raises the temperature then this is SHC. If the state changes then this is SLH. Plates are flat. The word plateau has plate in it. So remember that a plateau is like a flat plate!

5. www.PhysicsGCSE.co.uk Specific Heat Capacity Calculations Important! Different substances have different SHC values. The higher the SHC value then the more energy needed to raise its temperature. A higher SHC also means a longer time to heat up. SHC: Energy transferred = mass x SHC x temperature change Calculate the energy transferred when 60 kg of seawater is heated from 15°C to 70°C. Energy transferred = mass x SHC x temperature change Energy transferred = 60 kg x 3900 J/kg°C x (70°C-15°C) Energy transferred = 60 x 3900 x 55 Energy transferred = 12870000 J = 12.87 MJ So water requires more energy to raise its temperature as it has the largest SHC value in this table

6. www.PhysicsGCSE.co.uk Specific Latent Heat Calculations Substances require different SLH values to change state. A higher value means that more heat energy is needed to be absorbed (if heated up) or released (if cooling down) to change that state. Important! SLH: Energy transferred = mass x specific latent heat Calculate the energy transferred when 1.25kg of ice melts at 0° Energy transferred = mass x specific latent heat Energy transferred = 1.25kg x 340,000 J/kg Energy transferred = 425,000 J = 425 kJ So water requires more energy to be absorbed to change from liquid to gas than solid to liquid Remember there is no temperature change in the calculation. The 0°C information is telling you that you are dealing with a solid. Recall that water is a solid (ice) at 0°C

7. www.PhysicsGCSE.co.uk Quick Questions • Eve says that when you heat an object it gets hot. Adam says it does not. Explain who is right. • The SHC of quartz glass is 700 J/kg °C. How much energy is needed to raise the temperature of 1kg of quartz glass by just 1 °C? • A graph shows a substance melting and then boiling. Where on the graph would you locate where the substance is changing state? • An aluminium saucepan has a mass of 2.4kg. How much energy is needed to raise its temperature from 22 °C to 100 °C so it can boil some water?

8. www.PhysicsGCSE.co.uk Quick Questions • Eve says that when you heat an object it gets hot. Adam says it does not. Explain who is right. Both are correct: Eve is correct when discussing an object that is not changing state. Adam is correct when discussing an object that is changing state. • The SHC of quartz glass is 700 J/kg °C. How much energy is needed to raise the temperature of 1kg of quartz glass by just 1 °C? 700J • A graph shows a substance melting and then boiling. Where on the graph would you locate where the substance is changing state? This is where there is a plateau (remember plateau is the straight plate part) • An aluminium saucepan has a mass of 2.4kg. How much energy is needed to raise its temperature from 22 °C to 100 °C so it can boil some water? Energy transferred = mass x SHC x temperature change Energy transferred = 2.4kg x 897 J/kg °C x 78 °C Energy transferred = 167918.4 J = ~ 168kJ