2. Latent heat,
During a change in state the heat energy flow is used to change the bonding between the molecules. In the case of melting, added energy is used to break the bonds between the molecules. In the case of freezing, energy is given out as the molecules bond to one another, into less energetic states. These energy exchanges are not changes in kinetic energy. They are changes in bonding energy between the molecules.
Latent heat is the heat energy supplied to a substance to change state. There is no rise in temperature at this stage.
use Cetyl Alcohol to plot the
http://www.seai.ie/Schools/Post_Primary/Subjects/Physics/Unit_5_-_Heat_Quantity/Latent_Heat/
The STS of Latent Heat (Applications)
specific latent heat
Definitions and units.
Appropriate calculations.
In order to extract the maximum flavor in the shortest amount of time, your local fast food purveyor has decided to brew its coffee at 90 ℃ and serve it quickly so that it has only cooled down to 85 ℃. While this may be economically sensible, it is negligent and dangerous from a health and safety standpoint. Water (which is what coffee mostly is) at 85 ℃ is hot enough to cause third-degree burns (the worst kind) in two to seven seconds. You decide to add ice cubes to your coffee to cool it down to a more reasonable 55 ℃ so you will be able to drink it sooner. (Watery brew be damned. You need your caffeine now.) How many 23.5 g ice cubes at −18.5 ℃ should you add to your 355 ml cup of coffee to accomplish your thermal goal?
3. Measurement of the specific latent heat of fusion of ice.
Heat experiment 2 Latent heat of fusion
http://www.sei.ie/Schools/Secondary_Schools/Subjects/Physics/Unit_5_-_Heat_Quantity/Experiment_2/
The ice is added to water above room temperature because
The Ice is crushed as a large block of ice would have a colder core temperature than the outside
The ice is dried as to measure only the latent heat of ice, without adding excess water that woujld distort the readings
Common Sources of error
Thermometer takes heat out
Lack of insulation
Spillage of water
Ice not crushed / dried
4. Measurement of the specific latent heat of vaporisation of water.
Heat experiment 3 Latent heat of vaporisation
Heat pump,
https://www.youtube.com/watch?v=UbcoeHiJFFY
Homemade heatpump pic here !!!
needs editing!!
A fridge works using a heat pump. This system allows a liquid that has a low boiling point (this means it will readily turn into a gas) to be pumped around a coil. When the liquid enters the less presurised part of the system, it expands, it turns into a gas. This lower pressure, lowers the boiling temperature of the coolant. The liquid boils at a lower temperature at the lower temperature.
The change of state still requires energy, and so the coolant liquid takes in the energy from the air surrounding it, the fridge.
It is essential that you understand that even if something is cool or even cold it still has heat energy. Some of the remaining heat energy in the cold volume of a fridge or freezer is given to the coolant, thus further removing the heat from the cool region.
This coolant however must complete a cycle and so is taken out of the insulated unit and is compressed back into a liquid, as we can see from the diagram above this releases energy in the form of heat out the back of the unit.
The fridge cools slowly.
The same effect can also be used to heat a space, if you can remove heat from somewhere and relocate the energy somewhere else this can reduce heating costs. The 'social housing' project the Oliver Bond flats on the Quays (behind the petrol station) was supposed to be heated using this type of heat pump. In the early 1970's the council objected to using the 'heat' from the River Liffey. Now it is becoming a standard low running cost and maintainance method of heating homes.
Fridges
https://brilliant.org/practice/how-does-a-refrigerator-work/
A Question
Mid-ocean ridges and other volcanic areas emit a large amount of energy due to the cooling of magma. In this question you will calculate the amount of energy that could be obtained from this source. The answer will depend on how much lava there is, its initial temperature and its physical properties (such as specific heat capacity and the specific latent heat of solidification).
Consider a particular example of a lava flow with a volume of 5.2 × 107 m3 and a density of 2.7 × 103 kg m–3 which erupts at a temperature, Terupt, of 1145 °C and cools to a final temperature, Tfinal, of 10 °C. Assume that the specific heat capacity, c, of both the lava and the rock formed is 1.5 × 103 J kg–1 °C–1, and that the average specific latent heat, L, released from the lava in solidifying into a crystalline rock is 4 × 105 J kg–1.
(i) Calculate the mass, m, of lava. (Show all of your working.) (ii) Write an equation, using symbolic notation, expressing the total energy, q, released from the lava as a result of cooling and crystallisation.
(iii) Calculate the total amount of energy, q, released by the lava. (Show all of your working.)
Check Out the Mpenda effect especially the guy that it is named after ...
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