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Tue 19 Dec, 2006 04:09 pm
Hey, I need help with these few questions for As Physics:
1) Calculate the heat required to convert 2kg of ice at -12 degrees C to steam at 100 degrees C.
2) Calculate the quantity of heat required to melt 4kg of ice at 0 degrees C and to raise the temperature of the water formed to 50 degrees C.
(Take the specific latent heat of ice to be 3.4x10^5 J/Kg and the specific heat capacity of water to be 4.2x10^3 J/KgK.)
3) What is the shortest time for which a 2.5kW kettle containing 1.5kg of boiling water can be left without boiling dry? (Take the specific latent heat of vaporization of water as 2.26x10^6 J/kg).
4) A refrigerator can convert 400g of water at 20 degrees C to ice at -10 degrees C in 3 hours. Find the average rate of heat extraction from the water in joules per second.
You should do your own homework. That's how you learn things.
Hey all I asked was for some help so that I can work my way forward from there, not to be told that thank you, or shall I say no thank you
I was told that this site would help me if I needed it, by educated people who know what they are talking about. My college wont be happy about the post, it does not point me in the right direction in the slightest.
There are two processes (and related physical parameters) that you must consider;
1. The amount of heat required to melt a mass unit of ice at a constant temperatuire (the freezing or melting point). This is the energy required to break the crystalline bonds associated with the previous freezing of the liquid. It is called the 'Latent Heat of fusion, There is also another parameter for the Latent heat of Vaporization, which is the heat requiired to break the liquid bonds and produce steam - also at constant temperature,
2. The amount of heat required to raise the temperature of water one degree Farenheidt or Celsius. This is the energy required to excite the water molecukes to the average energy level associated with the higher temperature. It is generally called the Specific Heat.
As a matter of practical fact the Latent Heat of Water is about 1000 times the Specific Heat. This is the key property of water that makes steam engines work so well.
Thank you. You've been most helpful.