Chemistry Questions

[Globex]

Is it possible for sugar to exist in a liquid or gaseous state? I know that sugar breaks down when heat is applied to it so is it possible to melt it or vaporize it without changing its chemical composition?

Can all substances exist in gas, liquid, and solid states or can some of them only exist in some states but not others?

 

[Perfection]

AFAIK, Sugar cannot exist as a gas. I think some smaller sugars (like glucose) can be liquid, but I'm not sure.

The big thing is it certainly isn't the case that all substances can exist as gases, liquids, and solids. It as you note the case that sugar is broken down by heat, this makes it not have a gaseous state.


One more thing I should note is that the three states of mater as solid, liquid and gas is just an approximation, there are plenty of substances that don't act exactly like any of the three.

 

[Dubai Vol]

Is it possible for sugar to exist in a liquid or gaseous state? I know that sugar breaks down when heat is applied to it so is it possible to melt it or vaporize it without changing its chemical composition?

Can all substances exist in gas, liquid, and solid states or can some of them only exist in some states but not others?

Fun question. Chemistry was a while ago but I rem a bit.

First, it's important to define terms. A 'substance' can be anything from a single element to a complex molecule. In general terms, the more complex the substance, the less stable it is, and will break down more easily.

From memory, simple sugar is C6H12O6 which is hardly complex, but not as simple as a pure element. There is also the issue of energy states. Sugar can be oxidized to release energy, because it took energy to form the molecule.

i won't try to write the equation, but basically the hydrogen and carbon in the sugar molecule combine with oxygen to produce CO2 and H2O plus energy.

The water and carbon dioxide molecules are very stable becasue they are low in energy, speaking in thermodynamic terms (and not very scientific ones, but let's not quibble.) You can't "burn" water or carbon dioxide: there is no chemical energy left to release. It all got burned when you oxidized the sugar.(Again, not rigorous, but in essence true.)

Long way around to say that while lots of substances exist in all three physical states, lots more are fragile and break down when you try to add or subtract energy from them. And even some elements never become solids. No such thing as solid hydrogen, no matter how cold you make it. Helium gets funky near absolute zero, but never solid either.

Absolute zero is defined as the point at which no more heat energy can be removed. It's a theoretical thing. If I'm not mistaken, nothing can actually get there. -273.15C

I'll defer to real experts now, but thanx 4 asking. Can you tell I enjoyed chem back in the day?

 

[Mise]

@Dubai Vol:
http://en.wikipedia.org/wiki/Solid_hydrogen

http://en.wikipedia.org/wiki/Metallic_hydrogen

these might interest you ^^

@Perf:
Can't you melt and boil sugar by applying dry heat in an oxygen-free environment? Or does "broken down" mean turn to smaller compounds, rather than "burn"?

 

[uppi]

No such thing as solid hydrogen, no matter how cold you make it. Helium gets funky near absolute zero, but never solid either.

Its actually pretty easy to solidify hydrogen. The melting point at standard pressure is around 14K and that's pretty easy to reach.

Helium does not solidify at standard pressure, but once the pressure gets high enough solid helium does exist.

Absolute zero is defined as the point at which no more heat energy can be removed. It's a theoretical thing. If I'm not mistaken, nothing can actually get there. -273.15C

True. One can get pretty close, though. I think the lowest temperature record is in the picokelvin range. That's 10^-12 K.

 

[El_Machinae]

Sugars could autocatalyse to break down into smaller compounds. Your body 'burns' sugar, even in oxygen-free environments.

 

[Perfection]

@Perf:
Can't you melt and boil sugar by applying dry heat in an oxygen-free environment?

No

Or does "broken down" mean turn to smaller compounds, rather than "burn"?

Well, it dos break into smaller componants. Whether it "burns depends on what you call "burn", I'd say. Sugars follow the formula: CxH2xOx. Oxygen prefers to be bonded to hydrogen over carbon, and if you get enough heat the following reaction will occur CxH2xOx --> xC + xH2O. It's sort of an incomplete self combustion, I suppose.

 

[Mr. Blonde]

The answer to your question is: not all substances may exist in all forms. The reason for this is that certain chemical reactions (in the case of sugar dehydratisation = sugar molecules break down into water and other products - it´s not a form of combustion which refers to oxidation processes) can happen before the phase transition (especially to gaseous). Point being is that conditions that drive evaporation (elevated temperature, low pressure) also drive breakdown reactions (formation of small, gaseous molecules).
Sugar may possess a certain gas pressure at temperatures where it doesn´t decompose, but it is probably so tiny that you can not make sugar boil (= vapour pressure is higher than outside pressure) with existing equipment.

 

[Perfection]

So wait is TNT detonation a combustion reaction?

 

[MrCynical]

So wait is TNT detonation a combustion reaction?

Nope. TNT is C7H5N3O6, which will decompose to 2.5H2O, 1.5N2, 3.5CO and 3.5C on detontation. No additional oxygen required.

 

[Perfection]

So an additional oxidizer is requirement rather then something oxidizing itself.

Interesting.

 

[Bartleby]

According to the Aldrich caltalogue, sucrose melts at 185°C.
I'm not saying you can, but I wouldn't be that surprised if you could sublime it in vacuo.
Sublimation is the process of converting a substance from solid form to gaseous form and back (or vice-versa), without going through an intermediate liquid phase.