Dry Ice

[muhali3]

The concept of solid turning into a gas is pretty hard for me to understand. It makes sense when i look at the phase-diagram of CO2, but if i try to picture it in my head its confusing. So after some thinking about Dalton's Law, Charles Law, and PV=nRT, i concluded that the boiling point of CO2 is lower than its melting point. Would that be correct? Does the relatively low pressure of 1 atm automatically cause the molecules to divert far away once the crystalline structure has broken? im asking these questions cause i have a test tomorrow and want to understand everything.

 

Thanks

[H2SO4]

He posted this a few days ago and didnt get any replies. Sucks for him becasue he didnt get the answer for his test. Tuff luck.

[budullewraagh]

im sorry. the CO2 is very uniform at lower temperatures, but with an increase in temperature, it boils just because there are weak intermolecular forces. as a result, the CO2 molecules break off as a gas

[Auburngirl05]

Try Googling "sublimation".

[mezarashi]

Well the fundamental thing to understand here is that you should not take the 3 states of water (solid, liquid, gas) that we as humans experience on a daily basis at what we consider to be normal temperatures and take them for granted. Other elements do not take on the same properties. The state of any compound depends on mainly two things, temperature and pressure. The atmospheric pressure as experienced on Earth allows for water to exist in three phases, If the atmospheric pressure was however below 0.5 atm, you will find that water too will also sublimate. Go from ice to vapor. Carbon happens to do that at 1.0 atm, so it seems unusual to us. Studying the phase diagrams will help you understand things better. A bit too late, but I hope you did well on that test XD

[jdurg]

Elemental Iodine is another good example. It will only form a liquid at an elevated local pressure. (I say local, because I had a large mass of iodine which was heated by a normal butane torch in a glass tube. As the heat was applied, there was rapid sublimation followed by the formation of liquid iodine. There was plenty of iodine there to see how it turned into a viscous liquid. REALLY neat to see. I didn't expect that to happen, but I guess the pressure at the surface of the iodine was high enough due to all the sublimated [math]{I_2}[/math]).