Let's say I have a flask...

[SaltyNuts]

And inside said flask there is a liquid that boils at call it 150 degrees Celsius. I put said flask with said liquid in a big pot of water on the stove. I turn heat up high. At 100 the water starts to boil. But I do not think the temperature of the water ever goes above 100. The more heat just causes the water to boil away faster and faster.

Here is the question: Will the liquid in the flask go above 100 and eventually hit 150, even though the water is never going above 100?

Thank you.

 

[dullard]

No, not until the bulk of the water has boiled off.

 

[Paperdoc]

You are exactly correct. The water in the pot will boil at 100C and continue to do so until it is ALL gone. AFTER that what remains in the pot (air) can get above 100C. As long as there is water in the pot, ALL of the heat energy applied from the stove burner (except what escapes into the surroundings) goes into converting water liquid into water vapour which floats away into the room, and there is NO temperature increase above 100C.

As a result of this, the material inside the flask experiences a constant surrounding temperature of exactly 100C as the water boils. Thus it can NEVER exceed that temperature, because heat can flow into it only from a HIGHER temperature source.

This is exactly the principle in using a double boiler pot for cooking - the item you are cooking in the upper pot never gets hotter than 100C, which prevents its sensitive ingredients from burning. The same concept is used in sous vide cooking - place the food in a bag, remove the air and seal, then immerse in boiling water. The items will cook slowly at exactly 100C as long as the water boils.

Decades ago I forgot all this and tried to make fudge in a double boiler. To do that you MUST raise the temperature of the sugar/milk/etc. mix well above 100C to convert the ingredients to the proper mix of fudge components, and you use a candy thermometer to monitor the temperature and judge when to quit cooking. When you do this in a regular pot directly on the burner, the fudge mix loses water and changes its chemical composition substantially as it boils, raising its Boiling Point temperature.But in my double-boiler event, the fudge-to-be mix never went over 100C! THEN I remembered why!

This also links to a common error in cooking by boiling. When doing that (say, boiling a pot of potatoes), many people will keep the burner up at highest setting to make the potatoes cook faster. BUT inside the pot, the potatoes only experience a temperature of 100C at all times as long as there is water boiling in the pot, no matter what the stove burner setting is. A high burner setting merely means that the water will boil away faster and there will be a higher rate of steam leaking out from the lid. This does NOT speed up cooking the potatoes. You only need the burner setting to be high enough to keep the water just boiling.

 

[IronWing]

Let's say I have a flask...

This is the most plausible explanation provided to date.

 

[brianmanahan]

let's say i have an airplane on a treadmill

 

[fralexandr]

You can increase the temperature of the flask in a water bath beyond 100°C with a pressurized/sealed system, ie a pressure cooker/canner, since PV=nRT

 

[nakedfrog]

I have a flask.

 

[dullard]

The same concept is used in sous vide cooking - place the food in a bag, remove the air and seal, then immerse in boiling water. The items will cook slowly at exactly 100C as long as the water boils.

If you set a sous vide meat dish to 100°C, then please don't ever let me eat your cooking. 53°C to 54°C for me. Then finish it at high heat to sear the sides.

 

[mpolo]

Hmm, steam can go above 100 deg c and the boiling water will contain bubbles of steam. I'd think at a rolling boil that the steam bubbles might push the temp of the liquid in the flask over 100. I'm guessing that the steam bubbles hitting the flask will give the latent heat of going back to liquid into the flask.

 

[dank69]

Demonstration:

 

[SaltyNuts]

Demonstration:

What in the actual hell? That is not relevant AT ALL. LOL.

 

[SaltyNuts]

You are exactly correct. The water in the pot will boil at 100C and continue to do so until it is ALL gone. AFTER that what remains in the pot (air) can get above 100C. As long as there is water in the pot, ALL of the heat energy applied from the stove burner (except what escapes into the surroundings) goes into converting water liquid into water vapour which floats away into the room, and there is NO temperature increase above 100C.

As a result of this, the material inside the flask experiences a constant surrounding temperature of exactly 100C as the water boils. Thus it can NEVER exceed that temperature, because heat can flow into it only from a HIGHER temperature source.

This is exactly the principle in using a double boiler pot for cooking - the item you are cooking in the upper pot never gets hotter than 100C, which prevents its sensitive ingredients from burning. The same concept is used in sous vide cooking - place the food in a bag, remove the air and seal, then immerse in boiling water. The items will cook slowly at exactly 100C as long as the water boils.

Decades ago I forgot all this and tried to make fudge in a double boiler. To do that you MUST raise the temperature of the sugar/milk/etc. mix well above 100C to convert the ingredients to the proper mix of fudge components, and you use a candy thermometer to monitor the temperature and judge when to quit cooking. When you do this in a regular pot directly on the burner, the fudge mix loses water and changes its chemical composition substantially as it boils, raising its Boiling Point temperature.But in my double-boiler event, the fudge-to-be mix never went over 100C! THEN I remembered why!

This also links to a common error in cooking by boiling. When doing that (say, boiling a pot of potatoes), many people will keep the burner up at highest setting to make the potatoes cook faster. BUT inside the pot, the potatoes only experience a temperature of 100C at all times as long as there is water boiling in the pot, no matter what the stove burner setting is. A high burner setting merely means that the water will boil away faster and there will be a higher rate of steam leaking out from the lid. This does NOT speed up cooking the potatoes. You only need the burner setting to be high enough to keep the water just boiling.

Thank you kind sir!!!

 

[SaltyNuts]

Hmm, steam can go above 100 deg c and the boiling water will contain bubbles of steam. I'd think at a rolling boil that the steam bubbles might push the temp of the liquid in the flask over 100. I'm guessing that the steam bubbles hitting the flask will give the latent heat of going back to liquid into the flask.

So, I was thinking about that. Maybe when a water molecule bumps into another water molecule, the latter evaporates, preventing its temp from going above 100 in liquid form. But what if that first water molecule (and others) bumped instead to the flask first, could not its temperature go above 100, then the temperature of the liquid inside the flask also go above 100?

But, even if it COULD theoretically go above 100, I bet it would only be like to 101 or to 100.0001 or something like that, not close to the 150 degrees needed to cause the liquid inside the flask to boil, so its just more of a theoretical thing I suppose.

 

[dank69]

What in the actual hell? That is not relevant AT ALL. LOL.

Of course it is. It shows that water will prevent materials from exceeding 100C whether those materials are inside the water or surrounding the water.

 

[ElFenix]

boiling is a cooling process

 

[SaltyNuts]

Of course it is. It shows that water will prevent materials from exceeding 100C whether those materials are inside the water or surrounding the water.

They cooked an egg in the water. They never took the temperate of the egg or its liquid inside to show that it never went above 100. It is irrelevant. And I want 2+ minutes of my life back having wasted it on the stupid video LOL...

 

[Fenixgoon]

if the flask is in contact with the bottom of the pot, then it's possible it could heat to the boiling point of the contained liquid - just a matter of whether the heat input from the pot is greater than the heat extraction of the water. but if it's just suspended in the water, then no, it will not reach 150C, because the water around it is only 100C

 

[SaltyNuts]

if the flask is in contact with the bottom of the pot, then it's possible it could heat to the boiling point of the contained liquid - just a matter of whether the heat input from the pot is greater than the heat extraction of the water. but if it's just suspended in the water, then no, it will not reach 150C, because the water around it is only 100C

That is a good point Fenixgoon, didn't think about that, let's assume it never touched or was even very close to the bottom. The question is could the water ever on its own heat up the flask (and likewise the liquid inside the flask) above 100. It sounds like it could never do it in any material amount. But could it get it to 101 for example based on the logic I posted above?

 

[mpolo]

So, I was thinking about that. Maybe when a water molecule bumps into another water molecule, the latter evaporates, preventing its temp from going above 100 in liquid form. But what if that first water molecule (and others) bumped instead to the flask first, could not its temperature go above 100, then the temperature of the liquid inside the flask also go above 100?

But, even if it COULD theoretically go above 100, I bet it would only be like to 101 or to 100.0001 or something like that, not close to the 150 degrees needed to cause the liquid inside the flask to boil, so its just more of a theoretical thing I suppose.

Yeah, I think you're correct. There is also the fact heat transfer is bi-directional, so as much as you want to try to heat the flask, the flask will in turn will heat the water too. The system stabilizes right at 100 degrees.

This makes me think of the Technology Connections youtube video where he explains rice cookers. It uses this principle as a mechanism to control the power to the cooker.

 

[brianmanahan]

let's say i inflate my tires to sidewall

 

[dank69]

They cooked an egg in the water. They never took the temperate of the egg or its liquid inside to show that it never went above 100. It is irrelevant. And I want 2+ minutes of my life back having wasted it on the stupid video LOL...

The egg is not the point. The point is the plastic bag that doesn't melt despite hanging right above a campfire at ~600F

 

[MtnMan]

Did you not boil water in a cone made from paper over a Bunsen burner in high school chemistry lab?

Or do they actually bother with teaching actual science in school today?

 

[Captante]

Did you not boil water in a cone made from paper over a Bunsen burner in high school chemistry lab?

Or do they actually bother with teaching actual science in school today?

I suspect a lot of the "hands-on" chemistry (the only good part lol) has gone the way of auto-mechanics and metal shop classes in US public schools.

 

[Torn Mind]

The answer is no. In layman's terms, "Heat" travels in one direction. From hot to cold until there is an equilibrium .

Formally, this would require discussing laws of thermodynamics.

 

[Torn Mind]

This also links to a common error in cooking by boiling. When doing that (say, boiling a pot of potatoes), many people will keep the burner up at highest setting to make the potatoes cook faster. BUT inside the pot, the potatoes only experience a temperature of 100C at all times as long as there is water boiling in the pot, no matter what the stove burner setting is. A high burner setting merely means that the water will boil away faster and there will be a higher rate of steam leaking out from the lid. This does NOT speed up cooking the potatoes. You only need the burner setting to be high enough to keep the water just boiling.

Well, higher heat does influence the period where colder food is initially put into the container and thus brings the temperature of the water back down below boiling. If I'm cooking macaroni, the pot is gonna be subjected to high heat.