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Do Now

Do Now. Write down three thing you need to do to work safely in a science laboratory. Outcomes: Understand that different materials require different amounts of energy to increase their temperature. Know the equation. Be able to use the equation.

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Do Now

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  1. Do Now • Write down three thing you need to do to work safely in a science laboratory

  2. Outcomes: Understand that different materials require different amounts of energy to increase their temperature. Know the equation. Be able to use the equation. Be able to describe an experiment to measure heat capacity. Specific heat capacity

  3. Copy this Glossary • absorber – A material that takes in thermal radiation. • conduction – The method of heat transfer in solids. • conductor – A material that lets heat flow through it. • convection – The method of heat transfer in fluids, which occurs because hot fluids are less dense than cold fluids. • emitter – A material that gives out thermal radiation. • free electrons – Electrons in a metal that are free to move through the metal. • heat transfer – The flow of heat energy from a hotter area to a colder area. • radiation – Heat energy transferred by infrared waves. This method of heat transfer does not need particles.

  4. How does energy affect materials? Do different materials need the same amount of energy to increase their temperature by the same amount? To increase the temperature of 1kg of copper by 1°C, requires 390 J. To increase the temperature of 1kg of water by 1°C, requires 4200 J. Water and copper require different amounts of energy because they have different values for a property calledspecific heat capacity. It is the amount of energy required to increase the temperature of 1 kg of a material by 1°C. So, the specific heat capacity for water is 4200 J/kg°C and for copper is 390 J/kg°C.

  5. What is specific heat capacity? The specific heat capacity of a material is the amount of energy required to raise 1kg of the material by 1°C. It can be used to work out how much energy is needed to raise the temperature of a material by a certain amount: specific heat capacity temperature change energy = mass x x • Energy is measured in joules (J). • Mass is measured in kilograms (kg). • Temperature change is measured in °C. • Specific heat capacity is measured in J/kg/°C.

  6. Energy absorbed = Mass x Specific Heat capacity x Temp rise The Mr McT equation E = mcΔT Calculations using S.H.C. J kg J/kg/°C °C

  7. 0.5kg of olive oil is heated until its temperature rises by 120 K. If the specific heat capacity of olive oil is 1970 J/kg/°C, how much heat energy was used? Energy absorbed = Mass x Specific Heat capacity x Temp rise Energy absorbed = 0.5 x 1970 x 120 Energy absorbed = 118200 J For example

  8. 12V A V E A metal Practical

  9. Go through Practical worksheet Follow instructions. Take measurements and do calculations. All students must complete the lab sheet

  10. Measuring SHCs • Energy put IN to metal = voltage x current x time • Energy = mass x specific heat capacity x temp rise voltage x current x time = mass x specific heat capacity x temp rise Specific heat capacity = (voltage x current x time)/(mass x temp rise)

  11. Specific heat capacity example Using the specific heat capacity of water (4200 J/kg°C), how much energy is needed to increase the temperature of 600 g of water by 80°C in a kettle? Note: mass = 600 g = 0.6 kg specific heat capacity temperature change energy = mass x x energy = 0.6 x 4200 x 80 = 201 600 J

  12. Do now Specific heat questions Q5 June 2005

  13. Latent heat

  14. Learning today • Use the terms latent heat of fusion and give a molecular interpretation of latent heat • Describe an experiment to measure specific latent heats for ice • Test Sunday 1st April 2012 • I will collect your books on Monday

  15. Latent Heat

  16. Melting point Temp (°C) Time (mins) Latent heat In a change of state experiment, from the graph you will notice a flat spot the temperature of the salol stopped changing as the salol changed from a liquid to a solid.

  17. Specific Latent heat“latent” = “hidden” Why does this happen?

  18. Specific Latent heat - Copy When a substance changes from solid to liquid or from liquid to gas, it takes energy to change its state. Heat is needed to break the bonds or separate the molecules. The temperature remains the same. When a liquid changes back to a solid energy is released again as the bonds form again. solid to liquid increasing their potential energy instead of raising the temperature (kinetic energy liquid Melting point Temp (°C) solid Time (mins)

  19. Specific Latent heat - copy The specific latent heat of a substance tells us how much energy is needed to change the state of 1 kg of substance at constant temperature. Solid to liquid/liquid to solid or liquid to gas/gas to liquid

  20. Specific Latent Heat The specific latent heat of fusion(melting) of ice at 0 ºC, for example, is 330000 J.kg-1. This means that to convert 1 kg of ice at 0 ºC to 1 kg of water at 0 ºC, 330000 J of heat must be absorbed by the ice. All at 0°C 1 kg 1 kg 334000 J absorbed

  21. Specific Latent Heat Conversely, when 1 kg of water at 0 ºC freezes to give 1 kg of ice at 0 ºC, 330000 J of heat will be released to the surroundings. All at 0°C 1 kg 1 kg 330000 J released

  22. Specific Latent Heat -Copy Energy = mass x specific latent heat J kg J/kg E = mL

  23. Specific Latent heat LE = m L Do Now question 1 page 119

  24. Learning today • Use the terms latent heat of fusion and fusion and give a molecular interpretation of latent heat • Describe an experiment to measure specific latent heats for ice and steam • Test Sunday 1st April 2012 • I will collect your books Today

  25. Specific Latent Heat of Fusion Experiment • Readings required • Energy supplied by heater • Energy = Power x time • Time = • Energy = VIt • Mass of water • E = mL • Latent heat = Energy supplied . mass of water

  26. Specific Latent Heat of Fusion Experiment • Energy = Power x time • Time = • Energy = VIt = • Mass of water = • E = mL • L = E /m • Latent heat = Energy supplied . mass of water

  27. Task- Evaluation • What are the limitations in our method? • What solutions can you think of? • Why do we wait until the water is dripping? • Does all the heat come from the heater? • Does all the ice remain in the funnel? • Now do Q4 Nov 2005

  28. Markscheme 4 (a) • turn on heater and wait until water starts dripping in beaker • empty beaker & replace, start watch • stop watch & remove beaker at same time • record time • find and record mass of water in beaker (b) 60 x t = 120 x 340 t = 680 s (c) (i) ice gains heat from surroundings/ice falls through funnel (ii) lag or fit lid to funnel/place gauze in funnel bottom

  29. Specific Latent Heat of Fusion Experiment

  30. Latent heat Now do Nov 2005 Q5

  31. Specific Latent Heat of Vaporisation - Copy For water at its normal boiling point of 100 ºC, the latent specific latent heat of vaporisation is 2260000 J/kg. This means that to convert 1 kg of water at 100 ºC to 1 kg of steam at 100 ºC, 2260000 J of heatmust be absorbed by the water. vice verse for vapour to liquid All at 100°C 1 kg 1 kg 2260000 J input

  32. Specific Latent Heat of Vaporisation Conversely, when 1 kg of steam at 100 ºC condenses to give 1 kg of water at 100 ºC, 2260 kJ of heat will be released to the surroundings. All at 100°C 1 kg 1 kg 2260000 J released

  33. Specific Latent Heat of Steam

  34. Latent Heat

  35. Specific Latent Heat -Copy Energy = mass x specific latent heat J kg J/kg E = mL

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