Latent Heat Notes These areas have extra notes to help you. Make notes as we go along, always including these post-its

To define ‘latent heat’ To be able to measure latent heat Objectives Objectives BRONZE To define ‘latent heat’ SILVER To be able to measure latent heat GOLD To be able to explain why the temperature of a substance remains steady whilst changing state

A tube of length 1.2m contains 0.04kg of metal ball bearings. Lesson Link A tube of length 1.2m contains 0.04kg of metal ball bearings. It is then inverted causing an energy transfer as the ball bearings fall leading to an increase in the internal energy of the metal. This can be measured by the thermometer. 𝑔 9.81 ms-2 Describe the energy transfer occurring, assuming no energy lost to surroundings (2 marks) Derive the equation to calculate the energy transferred to the metal for ‘n’ inversions. (2 marks) Calculate the specific heat capacity (c) for the metal when the set up is inverted 60times and a temp change of 5K was recorded (3 marks) mcӨ = mgln soo…… c=gLn/Ө. Therefore c = 141.26. Best to do the answer for 2 first to help with 3. Surely there is a way to combine the SHC equation with another one for energy?

Engage Split the class in half Pick one of the points below then try to create the most detailed (yet correct!) definition of… You’re competing SEA Keyword use Hints 5mins. Then ‘do you agree with that? What would you change or add’? Can we add any keywords? We will have a discussion, so make sure you’re aware of the definition you’re not making! SAND Melting Point Boiling Point

Engage The melting point of a substance is the temperature at which the intermolecular bonds within a solid break down sufficiently to change the state of a solid to a liquid under atmospheric pressure. Challenge: What would happen to the boiling point of water if it was heated at a high altitude? The boiling point of a substance is the temperature at which the vapour pressure of the liquid equals the atmospheric pressure surrounding the liquid and the liquid changes into a vapour. I.e. is the temp. when the liquid has been saturated with thermal energy, any additional energy causes particles to escape; a vapour. You what?! Compare and contrast their answers. What misconceptions are there? Refer back to the structure of the particle model (gaps, ability to flow etc). Draw diagrams on board.

We will then explore each individual part Objectives Explore ENERGY IN (BONDS BREAK) ENERGY IN (BONDS BREAK) Task: Orange: release of latent heat. Blue: heat required to break the bonds! ENERGY RELEASE (BONDS FORM) ENERGY RELEASE (BONDS FORM) Copy this diagram down We will then explore each individual part

‘LATENT’ Explore It means ‘hidden’ or ‘concealed’ What do the blue parts show? ‘LATENT’ What does it mean? How about the red parts? It means ‘hidden’ or ‘concealed’ Copy this graph and write a small description of what it shows! What is happening during the red parts? Hints Compare and contrast their answers. What misconceptions are there? Remember the definition of the melting and boiling points. What needs to be broken/locked to change state? Extension: Suggest why this is happening!

Explore When solid is heated at its melting point… Latent Heat of… When solid is heated at its melting point… Atoms vibrate more causing them to break apart This requires energy so all the energy input goes into breaking fused bonds (not temp!) So energy is increasing BUT NO temp rise (it’s hidden….latent ….heat!). Atoms further apart? You’ve made a liquid! Fusion Vaporisation But what happens to that heat energy when you leave the liquid to cool down? Why is there no temp rise? When the liquid is cooling, the latent heat is released. This is because the liquid molecules slow down to they are moving slowly enough for the force bonds to lock the molecules together. Some of the latent heat released keeps the temp of the substance at the melting point until solidification has been reached Bond breaking also take energy. Any energy added at this temp goes to the bonds!

Explore Latent Heat of… When liquid is heated at its boiling point…(Now it’s your turn…) Fusion Atoms gain enough kinetic energy causing them to break further apart This requires energy so all the energy input goes into breaking fused bonds (not temp!) So energy is increasing BUT NO temp rise (it’s hidden….latent ….heat!). Atoms even further apart? You’ve made a gas! Vaporisation Why is there no temp rise? Compare and contrast their answers. What misconceptions are there? Refer back to the structure of the particle model (gaps, ability to flow etc). Draw diagrams on board. Bond breaking also take energy. Any energy added at this temp goes to the bonds!

Objectives Explore ENERGY IN (BONDS BREAK) ENERGY IN (BONDS BREAK) Task: Orange: release of latent heat. Blue: heat required to break the bonds! ENERGY RELEASE (BONDS FORM) ENERGY RELEASE (BONDS FORM) Add small diagrams next to the energy boxes to show what is happening on a particle level

Define Specific Latent Heat of Vaporisation (L->G) Is the energy needed to change the state of 1kg of a substance from liquid to gas without a change in temperature Specific Latent Heat of Fusion Is….

Work out the units for ‘l’! Explore ∆Q Change in energy m Mass ∆Q=ml l Latent heat Task Work out the units for ‘l’! Extension Which would be greater for a substance. S.L.H for vaporisation or fusion, and why? “l " Remember to use the correct l for the problem. Fusion for solid to liquid and vaporisation when liquid to gas

Progress Checker Identify Calculate the energy needed to melt 5000g of ice at 0˚C and then heat that melted ice to 50˚C Specific latent heat of fusion of ice= 3.36x105Jkg-1 Specific heat capacity of water= 4200Jkg-1K-1 Convert Rearrange

Progress Checker Identify Calculate the energy needed to melt 5000g of ice at 0˚C and then heat that melted ice to 50˚C Specific latent heat of fusion of ice= 3.36x105Jkg-1 Specific heat capacity of water= 4200Jkg-1K-1 We need to find the energy needed to melt the ice (Q1) and the energy needed to heat the ice (Q2) To melt 5000g of ice (5kg), we need to work out the energy to overcome latent heat of fusion: Q=ml Q1 = 5kg x 3.36x105Jkg-1 = 1.68x106J It’s now water, so to heat the water we use the value of ‘c’, so Q2= mcӨ = 5 x 4200 x 50= 1.05x106J Total Q= Q1 + Q2 = 2.73x 106J Convert Practice time: You have 30 mins to work on the questions on the hand out. If you finish early, create a question of your own! Rearrange

Practical Plan How can we measure the latent heat of fusion of water? In pairs How can we measure the latent heat of fusion of water? Discuss Task 1: Identify what variables we would need to control and which ones we would measure Task 2: Suggest equipment that we could use. Go to another group and discover their ideas. Compare Task 3: Draw the diagram of the set up you would use. Compare it with the one shown to you Practical Hint Polystyrene cup, ice (15g), warm water. The energy lost is the energy needed to melt the ice! Could we possibly use some warm water here? Task 4: What would be the equation? Extension: rearrange to get ‘l’ of the liquid

Wider Context Exam Question Change in energy Explain why a scald by steam at 100oC would much more painful than one by the same mass of liquid water at 100oC? (4 marks) m Mass l Latent heat Possible homework How quickly can it cool (reach equilibrium)?

Add missing information Wider Context Exam Question ∆Q Change in energy Explain why a scold by steam at 100 oC would much more painful than one by the same mass of liquid water at 100 oC? (4 marks) Water at 100 oC would transfer a set amount of energy into the skin, determined by the SHC of water The steam however would need to release the latent heat (of vaporisation) energy first (into the skin) As it changes from gas to liquid (condenses) Before its temperature decreases (another heat loss into skin) Therefore more energy is released into the skin by the steam (latent + cooling) than by the water (cooling) This extra heat would be more painful. m Mass Peer assess Swap and mark Add missing information WWW EBI

To define ‘latent heat’ To be able to measure latent heat Objectives Objectives BRONZE To define ‘latent heat’ SILVER To be able to measure latent heat GOLD To be able to explain why the temperature of a substance remains steady whilst changing state

Objectives Independent Study Create three questions of your own, using any of the data provided to you. Once written, answer it below with clearly identifiable steps