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Thermal Physics

Blazing goIITian

Joined:	5 Jun 2007
Post:	978

26 Jan 2008 20:31:33 IST

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281

P-T phase diagrams

None

sir, please explain the red part of both the graphs ...

why for substaces like water (which contract on melting), increase in temp. decreases pressure

and why for substances like CO2 (which expand on melting), increase in temp. increases pressure ??

These P-T phase diagrams are not included in my Board(Assam) Exam Course.. are they in IIT JEE and AIEEE syllabi ??? If not, i'll leave them as they confuse me a lot

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Soumen Goswami

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Joined: 10 Apr 2007

Posts: 1777

26 Jan 2008 22:29:45 IST

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The slope of the PT curve is determined by the Cllaussius Claperon equation, which isn't included in JEE syllabus. However, you can browse the internet for more resources dealing with this.

manivasagam

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Joined: 18 Jul 2007

Posts: 20

28 Jan 2008 16:44:20 IST

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In general except water all substance will contract on freezing . but only water will expands on freezing.for this reason the density of ice will be less than water.( I think you have seen the flim titanic if u notices clearly the ice floats in water and there fore the ice is visible to you if it not it will settle in bottom of the sea this will cause great disaster in marine life) This is the special and the lonely property of water.This due to the molecular arrangement and crystal structure of water

consider water at 30 degree celsius at atmospheric temperature if you cools down at 0 degree celsius it will be started changing in to ice.

consider another criteria,if water is at -4 degree celsius it may water or liquid which depends on the pressure in which the water is.

From the above example we can tell that with increase in pressure the temperature has to decrease in order to bring water from liquid state to solid state

NOTE:This special property of water is only during transformation from solid to liquid & vice versa. Not during boiling ie during the transformation from liquid to vapour& vice versa.All substance will obey same temp & press graph for boiling or condensation.

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