From: card 29/12/99 12:25:26 Subject: solids, liquids, gases. post id: 21337 Can a solid change into a gas without being a liquid inbetween? From: bart 29/12/99 12:27:34 Subject: re: solids, liquids, gases. post id: 21339 Its called sublimination From: Chris (Avatar) 29/12/99 12:28:17 Subject: re: solids, liquids, gases. post id: 21340 Yes. There is a name for this type of phase change - it might be "sublimation" but I can't remember and am prepared to be corrected. From: Chris (Avatar) 29/12/99 12:29:09 Subject: re: solids, liquids, gases. post id: 21342 But I wasn't prepared to be beaten to the punch! Quick fingers, bart! :o) From: bart 29/12/99 12:30:43 Subject: re: solids, liquids, gases. post id: 21343 but you spelt it right Chris From: card 29/12/99 12:33:44 Subject: re: solids, liquids, gases. post id: 21344 can all solids sublimate? From: bart 29/12/99 12:34:59 Subject: re: solids, liquids, gases. post id: 21345 No, an example is dry ice CO2, dry ice sublimes From: brad 29/12/99 13:29:28 Subject: re: solids, liquids, gases. post id: 21375 Card, your question was "Can all solids sublime?" Some materials break down before they reach melting or sublimation point. This is often because infra-red (heat) is a molecule shaker (that's how it warms things) and some molecules don't take too much shaking before they fall apart. Of the materials that can melt and boil without breaking down (and most simple substances can do this) I'd say that most could be made to sublime. The solid, liquid and gaseous state of a material have a relationship that can be described with a PHASE DIAGRAM, which has pressure and temperature as axes (axis pl.). If you fool around with the pressure (decrease it for most things) you could probably make most things sublime. Carbon dioxide is just one chemical that doesn't have a liquid state at normal pressures, so we most commonly cite it as something that sublimes! cheers, brad From: Karl Kruszelnicki (Dr Karl) 29/12/99 14:11:18 Subject: re: solids, liquids, gases. post id: 21400 Sublimation is what happens to the stuff of comets, as they come close to the Sun, karl From: steve(primus) 29/12/99 15:14:28 Subject: re: solids, liquids, gases. post id: 21430 You can see sublimation at work in your freezer with the disappearing ice cubes. The ice evaporates if you leave the icecube tray alone for a while. From: Trev(TAO)¿ 29/12/99 15:18:03 Subject: re: solids, liquids, gases. post id: 21433 also can anyone tell me why water expands when it gets frozen when as far as my limited knowledge on the subject stuff usually shrinks when it is cooled and expands when it is heated?? sorry if this has been asked before :-)> Trev(TAO) From: Terry Frankcombe (Avatar) 29/12/99 19:37:57 Subject: re: solids, liquids, gases. post id: 21634 What bart, steve and Karl are all saying is that most (?) simple substances have a triple point, a pressure and temperature at which the substance can exist as liquid, solid or gas. At pressures and temperatures below the triple point things sublime. From: Stephen Bosi 29/12/99 21:23:47 Subject: re: solids, liquids, gases. post id: 21693 also can anyone tell me why water expands when it gets frozen ?? This has been asked before, but I can't find it in the FAQs. Water molecules are highly polar (i.e. have charged ends), bent molecules. Because of these two facts, in the solid form, the molecules are forced into a highly "open" (lots of empty space) network structure. In the liquid state, the molecules are randomly arranged which doesn't allow the highly open network structure to form, so the molecules can sit closer together. In most common substances, the particles in a solid can adopt a compact structure which takes up less room than the liquid. From: RADIOHEAD 29/12/99 21:26:11 Subject: re: solids, liquids, gases. post id: 21695 Why does'nt Vodka freeze? From: bart 29/12/99 21:28:31 Subject: re: solids, liquids, gases. post id: 21697 The freezer isn't cold enough. From: Martin Smith (Avatar) 29/12/99 23:08:48 Subject: re: solids, liquids, gases. post id: 21773 I am pretty sure water will sublime at the correct temp and pressure. If you get a hold of a engineering thermodynamics book it will probably show the phase graph for water (becuase it is used in power stations). At a certain pressure and temp all three phases can exist. As said above, I presume the only thing that would stop something from subliming (??) given all possible conditions of pressure would be if it decomposed first. Martin Smith From: Dr. Ed G (Avatar) 29/12/99 23:54:30 Subject: re: solids, liquids, gases. post id: 21814 Water sublimes at various points below 0 Celcius in a vacuum, depending on how good the vacuum is (low the pressure is). From: Min-Zhao Lee 17/01/00 21:22:41 Subject: re: solids, liquids, gases. post id: 27056 I read somewhere that in cold places one can hang washing out to dry, at which point it freezes and the clothes dry out without actually becoming wet. I also read (earlier in the forum) that water can be made to freeze without gaining volume, if the dissolved air is removed. The reason why it shrinks at about 277 K eludes me though. From: Alan™ 17/01/00 21:35:00 Subject: re: solids, liquids, gases. post id: 27060 Crystal reorientation from one type of crystal structure to another, will cause changes in the crystal dimensions and hence the overall size of the crystals volume. From: Terry Frankcombe (Avatar) 17/01/00 22:17:51 Subject: re: solids, liquids, gases. post id: 27085 Water sublimes at various points below 0 Celcius in a vacuum, depending on how good the vacuum is (low the pressure is). Here comes Terry the Pedant again... Actually, the Triple point of water is 273.16 K, whereas 0° C is 273.15 K. So water can sublime above 0° C. From: Terry Frankcombe (Avatar) 17/01/00 22:21:39 Subject: re: solids, liquids, gases. post id: 27087 Crystal reorientation from one type of crystal structure to another, will cause changes in the crystal dimensions and hence the overall size of the crystals volume. Caught out Alan! 277 K is 4° C. It's to do with the length of a hydrogen bond, and how the structure is lost on melting. From: Alan™ 17/01/00 23:37:44 Subject: re: solids, liquids, gases. post id: 27120 Sorry Terry if I confused you. I was refering to solids in general and not specifically about water. This forum is un-moderated. The views and opinions expressed are those of the individual poster and not the ABC. The ABC reserves the right to remove offensive or inappropriate messages.