Tilted Forum Project Discussion Community  

Go Back   Tilted Forum Project Discussion Community > The Academy > Tilted Knowledge and How-To


 
 
LinkBack Thread Tools
Old 10-23-2003, 06:03 PM   #1 (permalink)
Crazy
 
chemistry guys

just wondering:
say you had a flask with some liquid in it, and you capped the flask but let a small opening. then if you heated the flask, allowed the liquid to boil and evaporate out of the flask, and then capped the flask and allowed it to cool, you almost create a vaccuum (assuming the glass was strong enough not to collapse in on itself) correct?
my question here is, would it be possible to create a complete vaccuum inside of the sealed flask, and if you did, what would the temperature be inside?
__________________
cough
maxero is offline  
Old 10-23-2003, 06:28 PM   #2 (permalink)
Upright
 
iirc:

from the heating, capping, and cooling, you do create lower air pressure. in addition, as long as your flask doesn't have any serious flaws, it can easily withstand a vacuum.

now - you could create a very close approximation to a vacuum by using a vacuum pump to remove nearly all of the air.

since temperature is really the measure of the state of excitement of atoms, since there aren't any atoms to measure i think the temperature would be considered absolute zero. however, it has been awhile since i took chemistry, so i may be wrong....
__________________
Truth is independant of Belief.
Jynx is offline  
Old 10-23-2003, 07:40 PM   #3 (permalink)
Psycho
 
Location: PA
There are no perfect vacua. Your hole would allow air in as well as vapor out. You actually couldn't get it below atmospheric pressure this way. Putting in hot air at atmospheric pressure, and then capping and cooling would give you low pressure, but it isn't very good compared to a vacuum pump.
stingc is offline  
Old 10-23-2003, 08:32 PM   #4 (permalink)
MSD
The sky calls to us ...
 
MSD's Avatar
 
Super Moderator
Location: CT
You can get enough of a vacuum to fill about 3/4 of a 2L flask by heating a small amount of water until it boils, then capping it with a stopper that has a hole in it, then inverting it and placing the stopper in a wide basin of water.
MSD is offline  
Old 10-23-2003, 09:09 PM   #5 (permalink)
Banned
 
Location: UCSD, 510.49 miles from my love
if you had a liquid in a flask, you could never approach a vacuum, because some of the liquids vapor would fill the emptiness in the air.

If you used a vacuum pump, however, and you were using some very robust vials, you could aproach a vacuum, and also have the temperature approach absolute zero, 0K, or -283C. You wouldnt be able to do this with your pyrex flask, it would definitely implode if the pressure got too low. The stopper probably wouldnt stay stopped either.

The same thing basically happens if you bring a drink on an airplane, to approximately the same degree as the boiling experiment.
numist is offline  
Old 10-23-2003, 11:55 PM   #6 (permalink)
Devils Cabana Boy
 
Dilbert1234567's Avatar
 
Location: Central Coast CA
Temperature is defined as the average kinetic energy of the atoms (or something like this) so if there were no matter there would be no temperature. Creating a perfect vacuum is practically impossible though.
__________________
Donate Blood!

"Love is not finding the perfect person, but learning to see an imperfect person perfectly." -Sam Keen
Dilbert1234567 is offline  
Old 10-28-2003, 12:24 AM   #7 (permalink)
Crazy
 
Location: some volcano in the middle of the pacific
Quote:
Originally posted by stingc
There are no perfect vacua. Your hole would allow air in as well as vapor out. You actually couldn't get it below atmospheric pressure this way. Putting in hot air at atmospheric pressure, and then capping and cooling would give you low pressure, but it isn't very good compared to a vacuum pump.
A good example of a perfect vacuum on earth is in a barometer. The mercury is heavy enough that at the top of the glass cylinder a perfect vacuum forms.

As for the temperature, the vacuum has no temperature, (no molecules = no temp) however if you were to put an object in the vacuum (technically no longer a vacuum) say a thermometer, that thermometer would be heated by infra red radiation given off by all molecules that have heat. IR radiation can pass through a vacuum ( sun heats earth by IR) and strike an object, converting the IR radiation to the kinetic energy that moves molecules and is in turn: heat.
matt_mll is offline  
Old 10-28-2003, 12:51 AM   #8 (permalink)
Psycho
 
Location: PA
Your perfect vacuum is not perfect. There is a bit of mercury vapor for example that will always be there. Again, a perfect vacuum is not possible on macroscopic scales.

To say that the vacuum has no temperature depends on your definition of temperature. The usual one that people throw around is kinetic energy of molecules. This is however not precise. E=n/2kT for n degrees of freedom, but this depends on "degrees of freedom" meaning a very specific thing which doesn't always hold. In any case, that formula (and its inadequacies) come from a deeper definition. Its fairly involved, so I won't get into it. The basic idea, though, is that objects are said to be at the same temperature if they can be brought into contact with one another without heat (non-mechanical energy) flowing between them. So matt_mll's radiation would actually be said to be at a certain temperature even without matter being present. Its just semantics though.
stingc is offline  
 

Tags
chemistry, guys

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On



All times are GMT -8. The time now is 04:05 AM.

Tilted Forum Project

Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
© 2002-2012 Tilted Forum Project

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360