Settle the Debate: Boiling Time of Water at Different Temperatures on Stove

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tammikec
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Here's the issue in question. Let's say you had two equally sized pans filled with equal amounts of water. The only difference between them is the water in one pan is 50 degrees while the other is 100 degrees. Next, they are put on the stove with equal flame applied, would the pan with 100 degree water come to a boil first or would they both come to a boil at the same time.
 
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The pan at 100 degrees (celsius or farenheit) would come to boil first. Classical heat equation Q=C*dT.
They both have the same mass and are both water so their heat capacity is the same. The heat energy applied to both (from the flame) is the same. So the temperature should go up at a similar rate in each. Since the 100 degree pan has distance to travel in this regard, it will reach boiling temperature first.
 
No, no equations necessary, you can solve this without knowing any science!
 
If they were both 100F, they would both take the same amount of time to boil, agreed?

So if the one that is 50F has to first go to 100F, the only way it can be faster is if it takes negative time to boil from 50 to 100, and that ant going to happen. See, no equations!
 
tammikec said:
Here's the issue in question. Let's say you had two equally sized pans filled with equal amounts of water. The only difference between them is the water in one pan is 50 degrees while the other is 100 degrees. Next, they are put on the stove with equal flame applied, would the pan with 100 degree water come to a boil first or would they both come to a boil at the same time.
Not only is it intuitively obvious that the pan with near-boiling water will boil first, but you can prove that it makes no sense otherwise.

Say a pan50F takes 10 minutes to boil.
We'll postulate that pan100F also takes 10 minutes.

So, now what happens when pan50F reaches 100F? It will now take 10 minutes from that point to boil. Which means it actually took 20 minutes in total. Which would mean 10=20!

Which is impossible, therefore the initial postulate can't be true.
 
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cyrusabdollahi said:
If they were both 100F, they would both take the same amount of time to boil, agreed?

So if the one that is 50F has to first go to 100F, the only way it can be faster is if it takes negative time to boil from 50 to 100, and that ant going to happen. See, no equations!
I've got one word for you: Mpemba!
 
I've got one for you, prove it! :wink:
 
No, no. It's a trick quesion. The OP craftily didn't specify whether the temperatures were in C or F. The 100C pan is already boiling before it is put on the stove, so neither answer is correct!
 
berkeman said:
No, no. It's a trick quesion. The OP craftily didn't specify whether the temperatures were in C or F. The 100C pan is already boiling before it is put on the stove, so neither answer is correct!
Boiling usually means that the water is turning into water vapor at a great rate.
At a lower rate its called simmering.
In any event 100c water isn't boiling without a heat input cause it would get less than 100c instantly.

Err, in a pan it's going to get colder instantly anyway:smile:
 
Water boils at a temperature slightly greater than 100C, despite popular belief. It has to be >100C for nucleation and bubbles to form.

"Simmering" is not a proper term, as far as I am aware.
 
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Ehh? That's equally wrong as well...water vaporizes(well, evaporates) at room temp, it does NOT boil.
 
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No, its not. Arg...you need to get a book on thermodynamics.

Boiling is for a solid-liquid interface.

Evaporation occurs at the liquid-vapor interface

Now, no more misuse of words. :smile:
 
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What...? :confused:

Do you think it all boils instantly into a vapor?
 
Ah, sorry. The solid is the pan, the liquid is the water.

Better?
 
:smile: Yeah, that was funny...do you see the difference now? They are not the same.
 
They are not the same, what don't you get?
 
I confess cyrus - not that this needs to be beaten to death any more - but it seems your're making the issue even more confusing.

"Evaporation occurs at the liquid-vapor interface"

"Boiling is for a solid-liquid interface."
"The solid is the pan, the liquid is the water."

By this, you seem to be indicating (and I'm sure you don't mean to) that the pan itself is boiling into the water.
 
cyrusabdollahi said:
Water boils at a temperature slightly greater than 100C, despite popular belief. It has to be >100C for nucleation and bubles to form.
Actually, I believe it is 99.97C at 1 atm.
 
cyrusabdollahi said:
No, its not. Arg...you need to get a book on thermodynamics.

Boiling is for a solid-liquid interface.
Boiling is the liquid-vapor phase change.

Freezing is the solid-liquid phase change

See enthalpy of fusion, enthalpy of vaporization

Evaporation occurs at the liquid-vapor interface

Now, no more misuse of words. :smile:
Hmmm
 

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