View Full Version : Latent heat
MrSparkle
2008-11-06, 15:24
I read the wiki article on latent heat but its still not clear to me. Lets say I heat some ice up and the temp gradually rises till it hits 0C then it starts melting. In my college notes they have a graph showing the temperature rise over time and when it gets to 0C it stops rising for a short amount of time so theres a straight line on the graph before it starts rising again. They say that flat line is the latent heat.
This is the graph
http://www.biophysics.uwa.edu.au/e_book/images/8cimg1.jpg
Yeah obviously if your just measuring the ice it won't rise about 0C but if you measured the melted water it could measure more than 0C couldn't it? Have I got this wrong? Will even the water around the ice stay at 0C until all the ice is fully melted?
Shadout Mapes
2008-11-06, 16:27
if the water got warmer it would transfer its heat to the remaining ice in the solution
MrSparkle
2008-11-06, 17:29
Oh yeah heat diffuses from areas of high temperature to cooler areas. I didn't even think of that thanks. Does this mean that a bucket full of water and ice will always be approximately 0C as long as you keep replacing the melted ice?
A little side question. How cold can things get? If I'm not mistaken heat is just atoms/molecules with a lot of kinetic energy. Conversely cold must be a lack of kinetic energy. Is there a point where the atoms just stop moving/vibrating altogether?
scovegner
2008-11-06, 17:39
Oh yeah heat diffuses from areas of high temperature to cooler areas. I didn't even think of that thanks. Does this mean that a bucket full of water and ice will always be approximately 0C as long as you keep replacing the melted ice?
A little side question. How cold can things get? If I'm not mistaken heat is just atoms/molecules with a lot of kinetic energy. Conversely cold must be a lack of kinetic energy. Is there a point where the atoms just stop moving/vibrating altogether?
Yep
http://en.wikipedia.org/wiki/Absolute_zero
Basically near-impossible to actually cool something down 0K, but scientists have got to within a couple billionths of a K ..
(K is just centigrade but it starts at absolute zero)
And yes,a bucket of ice/water should stay constant at 0C as long as there's enough ice etc to stop there being thermal gradients ..
MrSparkle
2008-11-06, 17:59
Thanks a lot that answers my question and more.
Mantikore
2008-11-08, 14:31
heres a chapter from my physics lecture notes at university about heat and energy. theres a bit about latent heat in there
http://rapidshare.com/files/161824165/Chapter_20.pdf.html