How does alchohol (we'll use ethanol for this example) behave in lower atmospheric pressures? Would it become volatile, or would it be less volatile and simply evaporate?

By volatile, we shall mean the tendency for a liquid substance to evaporate. It becomes more volatile, because of lower atmospheric pressure that counteracts the vapor pressure of ethanol.

Hi I was looking at the posts on fire paste in this forum ,that's the stuff invented by Troy Hurtubise that has very good heat insulating properties..I believe it is a geopolymer...with some organic components in it which causes holes in the ceramic during the curing process.Troy mentions that this material is made from diet coke and some low cost material that costs about 5 dollars per 45 gallon drum and that it would make people laugh if they knew what this material was.This material is I believe Fullers earth which is often used and sold as a kitty litter material because of it's absorbent properties.So two ingredients are diet coke and kitty litter (Fullers earth) the other ingredient which would make a geopolymer from the above two ingredients would then be either sodium bicarbonate or caustic soda.If bicarbonate of soda is used then the ceramic would cure at a relatively high temp.maybe around 400 to 600 deg C. If caustic soda is used the curing temp. would be considerably lower around 200 to 300 deg C.I made a really tough, light ceramic geopolymer from fullers earth, citric acid(diet coke ingredient) and bicarbonate of soda..I mixed the dry ingredients first and then added some water and pounded the stuff in a mortar and pestal till it was like a clay...the stuff fizzed first and then absorbed the water to become clay like..I formed the material into a little cube which I then cooked into ceramic on my gas stove top...the right combinations of fullers earth, citric acid powder and bicarbonate of soda powder will produce a good ceramic geopolymer without cracks that is light and tough and with very good heat insulating properties.

Mikal

And this has what to do with alcohol?

Nothing to with alcohol other than I had a beer after making a geopolymer on my kitchen stove from cheap ingredients I found in my local supermarket.I tried to start a new thread by putting 'fire paste' in the title but nothing came through for some reason.

Mikal

By volatile, we shall mean the tendency for a liquid substance to evaporate. It becomes more volatile, because of lower atmospheric pressure that counteracts the vapor pressure of ethanol.

Actually, 'volatile' was a poor choice of words on my part.
What I meant to ask was if it would lower the temperature required to cause it to ignite, or would it simply evaporate.

Actually, 'volatile' was a poor choice of words on my part.
What I meant to ask was if it would lower the temperature required to cause it to ignite, or would it simply evaporate.
Pressurized volatile compounds like alchohol would never evaporate under low pressure, remember higher pressure equals lower boiling point, and lower pressure equals higher boiling boint. Combustible compounds for instance like gasoline can explode if over pressurized in an engine. You can do this experiment yourself by putting alchohol in a pressure cooker and heat the mixture, most likely it will explode or evaporate at a low temperature, but it will never evaporate at low pressure or in a vacuum. Significantly, water boils easily at high pressures (low altitude), and takes forever to boil at low pressures(high attidudes). I'm not really sure about the alchohol, so look it up.

Pressurized volatile compounds like alchohol would never evaporate under low pressure, remember higher pressure equals lower boiling point, and lower pressure equals higher boiling boint. .... but it will never evaporate at low pressure or in a vacuum. Significantly, water boils easily at high pressures (low altitude), and takes forever to boil at low pressures(high attidudes).
You have that backwards, something will boil when its vapour pressure is above the atmosphearic pressure. That is, if I have water, and I take it to a sufficiantly high altitude it will 'spontaniously' boil. if I take it to a lower altitude (high preassure) it will take longer to boil. Boiling point increases with atmosphearic preasure.
Thus, if you want alchohol to not evapourate, increase the atmosphearic pressure.

Combustible compounds for instance like gasoline can explode if over pressurized in an engine. You can do this experiment yourself by putting alchohol in a pressure cooker and heat the mixture, most likely it will explode or evaporate at a low temperature
This is correct, and is how diesel engines operate, however the reason is that, under higher preassures the molecules are forced closer together, and thus more likely to react. The fact that tempurature increases with preassure also contributes.

-Andrew

The ideal gas law: PV=nRT.
Pressure times volume = number of moles times constant R times temperature.
I hope I've remembered tha correctly, I havn't used it since uni, and that was a few years ago.

andbna,
Here's the fact. Alchohol is volatile, and volatility is directly proportional to pressure. Therefore low pressure will result to nothing happening or more than likely a near freezing point since low pressure almost always equals low energy. A high pressure will result in quadropling the pressure in the system and possible ,though unlikely, explosion. You are mistaken with the altitude thing. A high altitude equals low pressure, and low pressure means the molecules are less tightly packed, which is why it takes longer to boil water. A low altitude means higher pressure(think deep sea) and a higher pressure means it takes shorter time to boil water (which is why using pressurized cooker to cook takes half the time).

You are mistaken with the altitude thing. A high altitude equals low pressure, and low pressure means the molecules are less tightly packed, which is why it takes longer to boil water. A low altitude means higher pressure(think deep sea) and a higher pressure means it takes shorter time to boil water (which is why using pressurized cooker to cook takes half the time).
No, boiling point increases as pressure increases and decreases as pressure decreases. You can cook things faster in a pressure cooker because the high pressure raises the boiling point, which means that the water is hotter (and therefore the food cooks fasters).

No, boiling point increases as pressure increases and decreases as pressure decreases. You can cook things faster in a pressure cooker because the high pressure raises the boiling point, which means that the water is hotter (and therefore the food cooks fasters).


You see, you are making a mistake. The boiling point of water is 100 degrees, but at high pressure water boils(evaporates) faster, which means it boils at about 90 degrees. Therefore high pressure lowers boiling point. :D

You see, you are making a mistake. The boiling point of water is 100 degrees, but at high pressure water boils(evaporates) faster, which means it boils at about 90 degrees. Therefore high pressure lowers boiling point. :D
Sorry, you just failed Chemistry 101. You have it exactly backwards. Read a chemistry textbook, or at least google it.

You see, you are making a mistake. The boiling point of water is 100 degrees, but at high pressure water boils(evaporates) faster, which means it boils at about 90 degrees. Therefore high pressure lowers boiling point. :D

Quite the opposite, Chatha. Lowering the pressure over ANY liquid will cause it to boil/evaporate faster/easier at a lower temperature. The key is something called "vapor pressure." (You might want to look up that term.)

And the reason for using pressure cookers is right in line with that. The goal of a pressure cooker is to increase the boiling point which allows the cooking water to reach a higher temperature. If you tried to cook a piece of meat on, say, the top of Pike's Peak, it not only would take forever but the meat would be undercooked. The pressure cooker is needed so that a high enough temperature can be achieved. (It's easy to see that you've never lived in Denver, Colorado.) ;)

I know what your problem is, I will help you understand. First you need to know that boiling point is the same as evaporating point. You see, the whole reason why things evaporate (escape) is because its too crowded inside the system, so when you increase the pressure of the system you will obviously increase the tendency of the molecules to evaporate. Water boils faster in a pressurized system because there is no way for the energy of the system to escape, it conserves energy, which is why it is able to evaporate or boil easily at temperatures around 95 degrees. The temperature of a pressurized system after 5 minutes will obviously be higher than an open system after the same time, but that does not mean that evaporation did not start at a lower temperature in a closed system. You are right, the goal of a pressure cooker is to increase the temperature by conserving energy, but that doeasn't mean water boils at 120 degrees in a pressure cooker, in fact water boils at about 95 degrees in a pressure cooker. Hence pressure decreases the boiling point of water and all other substances. Take a balloon and fill it with air then pierce it with a tiny pin, you will feel a lot of air escaping(evaporating) from the ballon. That means that you don't even need heat energy to make things escape when you have enough pressure. Thus pressure lowers boiling point, not increasing it. Low pressure cools things down, increasing the boiling point, thats why water boils at about 105 degrees in the mountains.

Quite the opposite, Chatha. Lowering the pressure over ANY liquid will cause it to boil/evaporate faster/easier at a lower temperature. The key is something called "vapor pressure." (You might want to look up that term Vapor pressure is the pressure exerted by a liquid when being heated, which when added with atmospheric pressure equals the total pressure. Lowering the pressure of a system will not cause it to boil faster, otherwise cooking with an opened pot will be faster than cooking with a closed one.

And the reason for using pressure cookers is right in line with that. The goal of a pressure cooker is to increase the boiling point which allows the cooking water to reach a higher temperature. If you tried to cook a piece of meat on, say, the top of Pike's Peak, it not only would take forever but the meat would be undercooked. The pressure cooker is needed so that a high enough temperature can be achieved. (It's easy to see that you've never lived in Denver, Colorado.) The goal of a pressure cooker is not to increase the boiling point as you say, but to conserve energy and increase the temperature in the system. Increasing the temp of the system is NOT the same as increasing the boiling point, otherwise water will boil at 150 degrees in a pressure cooker, which would be scientifically silly. Water will always boil around 100 degree regardless of the circumstance, but it will start to evaporate easily with increased pressure at constant temperature.

....allow me to clear something up so we can get back to pondering the effects on ethanol

http://www.youtube.com/watch?v=LxtAeGtL9SE&mode=related&search=

Hey---after reading the comments below the video, it looks like this is already used in "ethanol stills". I'll google around and look for more into on that

....allow me to clear something up so we can get back to pondering the effects on ethanol

http://www.youtube.com/watch?v=LxtAeGtL9SE&mode=related&search=

Hey---after reading the comments below the video, it looks like this is already used in "ethanol stills". I'll google around and look for more into on that

Certainly. Ethanol stills are as old as bootleggers and Prohibition. (Much older than that, actually.) ;) Ethanol has a higher vapor pressure than water and boils out of a mixture quite readily. Reducing the pressure in the receiver (condenser) allows the process to work at greatly reduced temperatures.

Vacuum distillation has many applications in the food industry and several others.

Water, like all liquids, starts to boil when its vapor pressure reaches its surrounding pressure. At higher elevations the atmospheric pressure is lower and water will boil at a lower temperature.
-http://en.wikipedia.org/wiki/Vapor_pressure

You see, the whole reason why things evaporate (escape) is because its too crowded inside the system, so when you increase the pressure of the system you will obviously increase the tendency of the molecules to evaporate.
Not quite, if I only increased the preassure of the water, then perhaps that would happen, but I can't do that. The corresponding increase in atmospheric preassure keeps the molecules in place as a liquid.

You are right, the goal of a pressure cooker is to increase the temperature by conserving energy, but that doeasn't mean water boils at 120 degrees in a pressure cooker, in fact water boils at about 95 degrees in a pressure cooker. I don't understand what you mean by 'conserving energy'?
Water does not boil at 95 degrees in a preassure cooker. If it did, the food would be sitting in a 95 degree liquid and cook more slowly than my stovetop which boils at 100 degrees.


Boiling, a type of phase transition, is the rapid vaporization of a liquid, which typically occurs when a liquid is heated to its boiling point, the temperature at which the vapor pressure of the liquid is equal to the pressure exerted on the liquid by the surrounding atmospheric pressure. Thus, a liquid may also boil when the pressure of the surrounding atmosphere is sufficiently reduced, such as the use of a vacuum pump or at high altitudes. Boiling occurs in three characteristic stages, which are nucleate, transition and film boiling. These stages generally take place from low to high surface temperatures, respectively. -http://en.wikipedia.org/wiki/Boiling

-Andrew

-http://en.wikipedia.org/wiki/Vapor_pressure


Not quite, if I only increased the preassure of the water, then perhaps that would happen, but I can't do that. The corresponding increase in atmospheric preassure keeps the molecules in place as a liquid. Actually you can, all you have to do is put a lid on the container, the weight of the lid is a function of the total pressure. Remember atmospheric pressure is nothing but the weight of the atmosphere.

I don't understand what you mean by 'conserving energy'?
Water does not boil at 95 degrees in a preassure cooker. If it did, the food would be sitting in a 95 degree liquid and cook more slowly than my stovetop which boils at 100 degrees. If you don't understand, just ask. A closed or pressurized system conserves energy because heat is not lost, but that's not the reason why water evaporates earlier, its because the molecules are packed too tightly together. When we say water boils at 100 degrees, thats just a general evaluation because water can and does boil at lower temperatures depending on the efficiency of the system. Water never boils at a higher temperature because there is no further heat loss or gain during phase transition (the process where water changes state). If you want water to have a higher boiling point, you have to mix it with something that has a higher boiling point, sort of like the same way adding salt to ice decreases its freezing point. Boiling point is the instant when one molecule of liquid water escapes as water vapor or gas, and the temperature always varies, just ask any scientist, but it never goes above 100 degrees.

<attempt at explanation that would get you an F in 9th grade science snipped>


Look, I've tried to be nice here, but you keep insisting that you’re right when it's clear that you have absolutely no f***ing idea what you're talking about. Read a basic chemistry textbook.

The vapor pressure of a liquid increases as temperature increases. If the vapor pressure of a liquid is greater than the atmospheric pressure around the liquid, that liquid will boil. That's why you have to heat water to boil it - you are heating it to raise its vapor pressure. If the atmospheric pressure is lower, then you don't have to heat the liquid as much to get it to boil because it doesn't have to attain as high a vapor pressure in order to start boiling. If you increase the atmospheric pressure on a liquid to above 1 atm, you now have to heat the liquid above 100 C to get it to boil. If you take a pot of water to the top of a high mountain, it will boil at less than 100 C because the pressure is lower. I don't know how I could make this any more explicit.

I went to some web sites and many seem to say a low pressure equals low boiling point and high pressure equals high boiling point. Sorry for the confusion guys. I think I was equating vapor point with boiling point or something like that.

Okay guys, I was on my way to work when I deciphered the root of our confusion. I am a chemistry undergrade and as a chemistry undergrade you get to work with a lot of standardization or STP's, and the STP of water is 100 degees at 1 atm. You get used to working with STP's so much that you use them all the time. The confusion is that I was using boiling point in relation to STP. I knew water boiled at lower temperatures at high elevation, which is why I said "increase the boiling point", but what I meant to say is that the water at high elevation will "need to increase its boiling point towards STP". It seems I was kind of thinking too far ahead each time, and I was further confused when you guys tried to correct me, which I mistakenly saw as a false arguement. Basicaly, all you need to know is that I was working towards or from STP. My mistake.

So as far as alchohol is concerned, alchohol will have a lower boiling point in a system of low pressure, alchohol is already very volatile so it most likely will disappear in low pressure.

I am a chemistry undergrade and as a chemistry undergrade you get to work with a lot of standardization or STP's, and the STP of water is 100 degees at 1 atm.

Try zero degrees.

Okay guys, I was on my way to work when I deciphered the root of our confusion.

One more minor correction right here. As to the statement above, there was NO "our confusion" - only yours.

I guess the only thing to say is ....oopsy daisy!:o

Try zero degrees.
Actually, I was talking about the normal boiling point of water. In Chemistry, the normal boiling point of water is the boiling point at 1 atm, which is 100 degrees celcius or 373k. But you should probably look it up in any text book (look up the "normal boiling point" of water) cause a lot of this stuff is too elementary that it sometimes confuses me.

It is a bit scary that there actually is a discussion about this. What happens when you take a flask of ethanol (use a round bottom flask or it may break) and attach it to a vacuum pump is that the ethanol starts to boil and the flask gets really cold on the outside. Pretty soon frost forms on the outside and boiling stops. Afrter a while the alcohol has evaporated. We professionals usually do this on a rotary evaporator where we rotate the flask slowly while putting it in a bath of warm water.

It is a bit scary that there actually is a discussion about this. What happens when you take a flask of ethanol (use a round bottom flask or it may break) and attach it to a vacuum pump is that the ethanol starts to boil and the flask gets really cold on the outside. Pretty soon frost forms on the outside and boiling stops. Afrter a while the alcohol has evaporated. We professionals usually do this on a rotary evaporator where we rotate the flask slowly while putting it in a bath of warm water.

Quite true and something quite commonly done to recover a substance that was dissolved in the ethanol. :)

It just seems that once in a while we encounter someone here who has his head wired backwards. That wouldn't necessarily be bad except the often become adamant about it - despite several people (including a few of us that are professionals) giving detailed explanations and examples to the contrary. It often becomes disheartening and sometime downright disgusting trying to get simple things through to them. (One chemistry or physics class in high school and they become immediate experts! Ugh!!!)

I am a chemistry undergrade . . . .

liar, or you would have never made the ridiculous claims in this thread.

Well, I never claimed to be an expert, and I am sure you don't even have to take college level chem to figure out this discussion. A lot of times I may become adamant over virtually anything, thanks partly due to endless arguements with people I know who get me mad(don't ask). As for whether or not i'm a chem major, that doesn't even really matter, unless you want to personally email me so I can give you my school ID so you can enquire an enrolment verification...blah! blah! blah!. Maybe you may also want to check my Business degree. For any info, i''m taking 300 level chem courses. Yes, some people here on sciforums can be annoying, thats a given. Some of these people make mistakes- not everybody truely enjoys intellectual discussions by typing over and into the internet. But some professionals here too can be annoying, they can't explain anything to save their life. A mentor of mine told me something that I would never forget, he said "how much you know about something is a function of how well you can teach it to anybody". That is the only fault I see from professionals here, but its probably because of the interface-internet forum. I make mistakes; big, small, medium, you name it. But even worse than me making mistakes is the fact that I may become adamant, which is a character I picked up but have totally stoped. Have the time I post on this forums, I'm either working or going to work, but almost always distracted, though that shouldn't be an excuse. Cheers