U.S. CitiesCity-Data Forum Index
Go Back   City-Data Forum > General Forums > Science and Technology
 [Register]
Please register to participate in our discussions with 2 million other members - it's free and quick! Some forums can only be seen by registered members. After you create your account, you'll be able to customize options and access all our 15,000 new posts/day with fewer ads.
View detailed profile (Advanced) or search
site with Google Custom Search

Search Forums  (Advanced)
 
Old 05-07-2014, 07:40 AM
 
2,480 posts, read 2,735,508 times
Reputation: 1096

Advertisements

What am I missing here? In "Origins", Mr. Tyson is talking about how water vaporizes at lower and lower temperatures as atmospheric pressure decreases. Using Mount Everest for his story, he reaches a point where liquid water (quote) "will 'boil' at 0 degrees -- that is, it will vaporize as soon as you expose it to the air." . He then goes on to say: "Scientists use the word ' sublimation' to describe the passage of substance from solid to gas without any intervening liquid stage."

My instant reaction: But water is a liquid. Granted it will vaporize as soon as we pull the plug on the container but it was in liquid state when it hit the air.

I am sure I am missing something. Please tell me what. Thanks.
Reply With Quote Quick reply to this message

 
Old 05-07-2014, 10:39 AM
 
Location: Somewhere in northern Alabama
16,873 posts, read 51,398,709 times
Reputation: 27766
Ice and snow are not liquid. They sublimate in the sun, even on below zero days. The heat from the sun provides sufficient energy to overcome the two energy roadblocks in one go - the heat required to transform solid (ice) to liquid and liquid (water) to water vapor. Surrounding ice can be solid while some molecules are bumped with enough energy.

FWIW, "freezer burn" is another example of sublimation. There is sufficient energy available even at freezer temps for the water in food to sublimate out into the dry air of the freezer.
Reply With Quote Quick reply to this message
 
Old 05-07-2014, 10:47 AM
 
2,480 posts, read 2,735,508 times
Reputation: 1096
Quote:
Originally Posted by harry chickpea View Post
Ice and snow are not liquid. They sublimate in the sun, even on below zero days. The heat from the sun provides sufficient energy two overcome the two energy roadblocks in one go - the heat required to transform solid (ice) to liquid and liquid (water) to water vapor. Surrounding ice can be solid while some molecules are bumped with enough energy.
I was referring to the water they tried to pour. Sorry if I didn't make that clear. They were carrying water up the mountain as part of their supplies. His point was that mountaineers have learned just how high you can carry water before it will no longer be of use to you since you can't pour it. At a certain height, it instantly "boils" to steam/gas.

That said, I think you've revealed what I was missing. The liquid never got a chance to interact with the air. The change was too instantaneous. Does that make sense? Does it work that way?
Reply With Quote Quick reply to this message
 
Old 05-07-2014, 04:54 PM
 
Location: Somewhere in northern Alabama
16,873 posts, read 51,398,709 times
Reputation: 27766
I'd guess that it had minimal chance to interact, but since the water was not solid, it doesn't meet the definition of sublimation. Don't expect programs on tv to be particularly accurate. I already commented on visual inaccuracies in that show and have no need to subject myself to it. At least least it isn't as bad as some of the episodes of Modern Marvels, which were complete misinterpretations and fabrications.
Reply With Quote Quick reply to this message
 
Old 05-07-2014, 05:03 PM
 
2,480 posts, read 2,735,508 times
Reputation: 1096
Quote:
Originally Posted by harry chickpea View Post
I'd guess that it had minimal chance to interact, but since the water was not solid, it doesn't meet the definition of sublimation. Don't expect programs on tv to be particularly accurate. I already commented on visual inaccuracies in that show and have no need to subject myself to it. At least least it isn't as bad as some of the episodes of Modern Marvels, which were complete misinterpretations and fabrications.
Actually, it's a book but it is a book reflecting the show, I suppose. Yes, if you are will versed in matters of astronomy, you probably would no enjoy the program but remember he is talking to the least of us. He knows how to talk to us without talking down to us as per my definition of an intelligent person.

This book is keeping me up until midnight every night. One night, the chapter was so good that I was still reading after 1:00 AM.

I'm not that slow a reader. It's just that I often have to read and re-read to be sure I got what he said.

That said, thank you about sublimation. I thought it was either a bit off-mark or scientists wanted to call it sublimation because the water never got a change to even start to interact. Good to have that straight. I wonder what they did for a good drink of H2O up there. Didn't have time to think about it, I imagine.
Reply With Quote Quick reply to this message
 
Old 05-07-2014, 08:28 PM
 
Location: Westwood, MA
3,477 posts, read 4,364,237 times
Reputation: 4477
Quote:
Originally Posted by Hazel W View Post
What am I missing here? In "Origins", Mr. Tyson is talking about how water vaporizes at lower and lower temperatures as atmospheric pressure decreases. Using Mount Everest for his story, he reaches a point where liquid water (quote) "will 'boil' at 0 degrees -- that is, it will vaporize as soon as you expose it to the air." . He then goes on to say: "Scientists use the word ' sublimation' to describe the passage of substance from solid to gas without any intervening liquid stage."

My instant reaction: But water is a liquid. Granted it will vaporize as soon as we pull the plug on the container but it was in liquid state when it hit the air.

I am sure I am missing something. Please tell me what. Thanks.
I'm not exactly sure what you're asking about, but understanding liquid-vapor transitions is really simple once you understand vapor pressure. Liquid water at a given temperature is in equilibrium with a fixed pressure of water vapor (the pressure is termed the vapor pressure). If the partial pressure of water vapor above a pool of liquid water is lower than the vapor pressure, some of the water evaporates and increases the partial pressure of water vapor until equilibrium is reached. If the partial pressure of water vapor above a pool of liquid water is greater than the vapor pressure, some of the vapor condenses (lower the partial pressure) until equilibrium is reached.

In a closed container, this process will move some of the water from the liquid to vapor phase and then stop. In an open container, however, the vapor is generally convected away, lowering the partial pressure of water vapor above the water, causing water to continually evaporate. This is why blowing air on something damp helps dry it more quickly.

This is where the concept of "relative humidity" comes from, as well. At 100% relative humidity, the partial pressure of water vapor in the atmosphere is equal to the vapor pressure of liquid water at that temperature. The lower the relative humidity, the faster water tends to evaporate.

The boiling point is simply when the vapor pressure is equal to atmospheric pressure. At the boiling point, water is no longer mechanically stable in the atmosphere and begins to expand directly into the vapor phase (we call this boiling). Boiling is not an instantaneous process, however, and typically requires some amount of time (and sometimes requires an activation energy, but that's not too important here), so to say it will instantly vaporize is incorrect.

Ice is also in equilibrium with a finite partial pressure of water vapor. In the same way as water, if the partial pressure of water above the ice is lower than this equilibrium vapor pressure, some of the ice will sublimate directly to vapor.

In general, both the water vapor pressure and the ice vapor pressure show a strong dependence with temperature, meaning that the boiling point shows a strong dependence on pressure. There is in fact a special point where the vapor pressures of both water and ice meet, a single pressure and temperature where ice, water, and water vapor exist in equilibrium together. This is called the triple point and can be used as a defining point for temperature scales.

I hope that a) makes sense and b) helps answer your question.
Reply With Quote Quick reply to this message
 
Old 05-07-2014, 11:25 PM
 
Location: Sarasota, FL
1,722 posts, read 1,833,734 times
Reputation: 1018
And a gallon of ice weighs less than a gallon of water. Science is crazy.
Reply With Quote Quick reply to this message
 
Old 05-08-2014, 05:57 AM
 
2,480 posts, read 2,735,508 times
Reputation: 1096
Quote:
Originally Posted by jayrandom View Post
I'm not exactly sure what you're asking about, but understanding liquid-vapor transitions is really simple once you understand vapor pressure. Liquid water at a given temperature is in equilibrium with a fixed pressure of water vapor (the pressure is termed the vapor pressure). If the partial pressure of water vapor above a pool of liquid water is lower than the vapor pressure, some of the water evaporates and increases the partial pressure of water vapor until equilibrium is reached. If the partial pressure of water vapor above a pool of liquid water is greater than the vapor pressure, some of the vapor condenses (lower the partial pressure) until equilibrium is reached.

In a closed container, this process will move some of the water from the liquid to vapor phase and then stop. In an open container, however, the vapor is generally convected away, lowering the partial pressure of water vapor above the water, causing water to continually evaporate. This is why blowing air on something damp helps dry it more quickly.

This is where the concept of "relative humidity" comes from, as well. At 100% relative humidity, the partial pressure of water vapor in the atmosphere is equal to the vapor pressure of liquid water at that temperature. The lower the relative humidity, the faster water tends to evaporate.

The boiling point is simply when the vapor pressure is equal to atmospheric pressure. At the boiling point, water is no longer mechanically stable in the atmosphere and begins to expand directly into the vapor phase (we call this boiling). Boiling is not an instantaneous process, however, and typically requires some amount of time (and sometimes requires an activation energy, but that's not too important here), so to say it will instantly vaporize is incorrect.

Ice is also in equilibrium with a finite partial pressure of water vapor. In the same way as water, if the partial pressure of water above the ice is lower than this equilibrium vapor pressure, some of the ice will sublimate directly to vapor.

In general, both the water vapor pressure and the ice vapor pressure show a strong dependence with temperature, meaning that the boiling point shows a strong dependence on pressure. There is in fact a special point where the vapor pressures of both water and ice meet, a single pressure and temperature where ice, water, and water vapor exist in equilibrium together. This is called the triple point and can be used as a defining point for temperature scales.

I hope that a) makes sense and b) helps answer your question.
I must be in good shape this morning. I really do understand what you are saying. And it all boils down to what I thought. There's a bit of a mis-statement in what I read. You can't say a solid went directly to a gas without an intervening liquid when it's a liquid that the gas came from. The only solid that I see is the container and the only place it is going is to rust whose futures is an iron mine.

Thanks. Have a good day.
Reply With Quote Quick reply to this message
 
Old 05-08-2014, 06:00 AM
 
2,480 posts, read 2,735,508 times
Reputation: 1096
Quote:
Originally Posted by beninfl View Post
And a gallon of ice weighs less than a gallon of water. Science is crazy.
Because a gas (air) invaded it? Would I be right? Only guessing.
Reply With Quote Quick reply to this message
 
Old 05-08-2014, 10:05 AM
 
Location: Sarasota, FL
1,722 posts, read 1,833,734 times
Reputation: 1018
Quote:
Originally Posted by Hazel W View Post
Because a gas (air) invaded it? Would I be right? Only guessing.
Nope..... When water freezes, the molecules arrange themselves to take up more space, so ice is lighter than water, and ice cubes float to the top of your cup instead of to the bottom.
Reply With Quote Quick reply to this message
Please register to post and access all features of our very popular forum. It is free and quick. Over $68,000 in prizes has already been given out to active posters on our forum. Additional giveaways are planned.

Detailed information about all U.S. cities, counties, and zip codes on our site: City-data.com.


Reply
Please update this thread with any new information or opinions. This open thread is still read by thousands of people, so we encourage all additional points of view.

Quick Reply
Message:

Over $104,000 in prizes was already given out to active posters on our forum and additional giveaways are planned!

Go Back   City-Data Forum > General Forums > Science and Technology
Follow City-Data.com founder on our Forum or

All times are GMT -6.

2005-2018, Advameg, Inc.

City-Data.com - Archive 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 - Top