Trivia Question for scientists and homemakers.

[Pure]

True or false: Hot water sometimes (some situations) freezes faster than cold water. For example in an icecube tray you put in your freezer.

{Added: yes we are assuming identical external conditions** [say, a freezer kept at 0 F] for, say, two identical non-huge containers of water. We are not discussing ponds, lakes, rivers, etc.}

PS: Anyone ever tried this comparison?

**Added: Hence we assume there is NOT a layer of ice beneath the vessels, which coats a cooling element; in such case, the hotter vessel may melt through the ice, bringing it in direct contact with the cooling element. This would be a trivial case of the 'hot water freezes faster' phenomenon.

 

[cheerful_deviant]

True or false: Hot water sometimes (some situations) freezes faster than cold water. For example in an icecube tray you put in your freezer.

Under the same conditions? Cold water will freeze faster. The water has to drop to 32 degrees (F) to freeze. If it starts off warmer, then it has farther to cool.

 

[English Lady]

Re: Re: Trivia Question for scientists and homemakers.

Under the same conditions? Cold water will freeze faster. The water has to drop to 32 degrees (F) to freeze. If it starts off warmer, then it has farther to cool.

sounds about right to me...

 

[snooper]

Let us say that the first sample starts at 68°F(20°C). Then it takes 10 minutes to reach 32°F(0°C) and then 5 more minutes to freeze. It has lost 36°F in ten minutes.

Consider a second sample exactly the same, except that it starts at 104°F(40°F). Since everything else is the same, the rate of loss of heat is the same and it will lose the necessary 72°C in 20 minutes and then take 5 minutes to freeze.

A more interesting question is, if you have a cup off coffee into which you have not yet put the cream/milk, will it cool faster if you put it in now, or wait a few minutes?

 

[NoJo]

I heard that if you boil water it gets rid of air bubbles, which can make it freeze fatser. Never tested this, as I'm not usually pressed for time when making ice cubes.

 

[Guest]

It has lost 36°F in ten minutes.

Noooooooooooooooooooooooooooooooooooooo

 

[Honey123]

Now I am curious.

If you keep opening the door, they don't freeze faster 'coz you're letting all the hot air in...so.....


(Sorry...had a blonde moment)

 

[dr_mabeuse]

All other things being equal, cold water freezes faster.

Boiling the water first drives out dissolved gases (gases are less soluble in warm solvent than in cold: witness pop going flat as it warms to room temp. The opposite is true of most solids, btw.) and will give you nice, clear ice cubes. At freezing, the creation of the ice crystals also drives out gases, which is why ice cubes are usually cloudy or opaque. (It's also why water derived from melted ice tastes so flat: no dissolved gases in it.)

Hot water cools at a faster rate than cold water though. The rate of cooling is a function of the heat differential between the liquid and its environment. Thus, water at 100 deg C, say, will drop in temperature more in ten minutes than water at 40 deg C. However, once the 100 deg water hits 40 deg, the cooling curves will be the same.

---dr.M.

 

[English Lady]

All other things being equal, cold water freezes faster.

Boiling the water first drives out dissolved gases (gases are less soluble in warm solvent than in cold: witness pop going flat as it warms to room temp. The opposite is true of most solids, btw.) and will give you nice, clear ice cubes. At freezing, the creation of the ice crystals also drives out gases, which is why ice cubes are usually cloudy or opaque. (It's also why water derived from melted ice tastes so flat: no dissolved gases in it.)

Hot water cools at a faster rate than cold water though. The rate of cooling is a function of the heat differential between the liquid and its environment. Thus, water at 100 deg C, say, will drop in temperature more in ten minutes than water at 40 deg C. However, once the 100 deg water hits 40 deg, the cooling curves will be the same.

---dr.M.

you learn something new every day Thanks Dr M!

 

[ABSTRUSE]

Okay, so when you boil a pot of water, they tell you to use cold. So, in the same essence wouldn't it make sense to use warm water as it would boil faster?...since the goal is to get hot water.

 

[English Lady]

When I boil a pan of water I always start out with hot water from the tap myself.....

 

[Guest]

When I boil a pan of water I always start out with hot water from the tap myself.....

I don't, I only use water from the cold tap for all cooking and drinking purposes. The water from the hot tap has been sat in a tank, and isn't drinking water.

Yes, I know boiling it will purify it, but what if there is even the slightest amount of sediment in it, or anything else that won't dissolve?

Maybe I'm just fussy.

 

[ABSTRUSE]

Now...do you salt your water before you boil it?

 

[Guest]

Altitude.

 

[Guest]

Now...do you salt your water before you boil it?

No, because I'd rather wait a bit longer for my water to boil, than risk putting too much salt in my family's diet. There's already way too much salt in food anyway (esp. breakfast cereals, bread and biscuits), so I think if someone wants to season their food, they can do it after it's on the plate.

High quantities of salt are very dangerous for kids, especially.

I sound like I'm on my high horse, don't I? LOL! I'm just careful and health conscious in the kitchen I guess - where cooking and preparing food is concerned, anyway.

 

[Lisa Denton]

If you put frozen french fries in boiling oil they explode (its o.k., I didn't get hurt) and it takes two days to clean up the kitchen.

 

[ABSTRUSE]

No, because I'd rather wait a bit longer for my water to boil, than risk putting too much salt in my family's diet. There's already way too much salt in food anyway (esp. breakfast cereals, bread and biscuits), so I think if someone wants to season their food, they can do it after it's on the plate.

High quantities of salt are very dangerous for kids, especially.

I sound like I'm on my high horse, don't I? LOL! I'm just careful and health conscious in the kitchen I guess - where cooking and preparing food is concerned, anyway.

I was just curious really, I read where it isn't really neccessary to do so and you're right about added salt. I stopped salting things when my mom found out she had Highblood pressure years back. I prefer to use various spices instead.
Hidden sugar is another thing to watch for, amazing when you start reading food lables and find out what's in them.

 

[Joe Wordsworth]

Originally posted by dr_mabeuse
All other things being equal, cold water freezes faster.

Not exactly true.

Hot water can and does freeze faster than cold water under some conditions, its called the Mpemba effect. Two containers, identical in every way and holding the same amount of water, have different temperature. They are placed in the same cooling situation and in some cases the warmer will freeze before the cooler one does.

We deal with this in basic Logic (around the time we cover Paradox), because it seems to be counter to what we can propose the situation to be. Most accurately put, its been observed and recreated a number of times dealing with evaporation factors, dissolved gas factors, convection factors, environmental factors, etc. Science doesn't really know why it happens in the cases (and there are a great number, consider that this question has been around since Aristotle) it does.

The short answer to the question is "Yes, sometimes, even if its counter intuitive, but no... 'why' is not definitely known".

 

[Guest]

It's all because of convection, isn't it?

Hot water has a lot more energy than cold water, so works a lot harder during the convection process, which pushes the heat up and out. This has a cumulative effect and the water cools at a much faster rate, making it freeze faster than the comparatively static cold water.

I do remember something about this from my dim and distant past, during a Physics 'A' level lesson. I might have listened a bit, while pissing about at the back of the classroom.

 

[dr_mabeuse]

Okay, so when you boil a pot of water, they tell you to use cold. So, in the same essence wouldn't it make sense to use warm water as it would boil faster?...since the goal is to get hot water.

If you're making tea or coffee, you don't want all the minerals that are dissolved in hot water (hot water picks up calcium salts from the pipes. That scale that forms on the bottom of the tea kettle is made of calcium salts. Calcium in water also forms a kind of scum with the tannic acid in tea), so you use cold. If you don't care about the taste of the water--if you're just cooking potatoes or pasta, for example--it doesn't matter what temperature water you use. I use hot because it takes less time to bring to a boil.

Salting water will make it take longer to boil (but not much) because dissolving almost anything in water will raise the boiling point, so instead of boiling at 100 deg C, it might boil at 105 or so. Dissolving anything in a liquid depresses the freezing point and elevates the boiling point (there are exceptions, called azeotropic mixtures). With the amount of salt we usually put into boiling water, the effect isn't very great. Maybe 2-5 deg C is all, unless you're using a heavy brine.

An interesting thing I learned about cooking using water is the idea that if you want to extract flavors from what you're cooking--if you're making soup or stew, for example--use cold water and bring it to the simmer with the meat in or veggies in it. This kind of extracts the flavors from the inside out.

If you're trying to keep the flavors in though, then put the food into boiling water. This cooks it from the outside in, and keeps the flavor components in the food, not in the water.

By the way, if you stare into a pot of water watching for it to boil, you can see the density gradient between the hotter, lghter water and the colder, heavier water. Those are called "Schlieren lines" after the German who studied them.

The noise water makes before it boils is due to the formation and collapse of microscopic bubbles of steam along the walls of the vessel. When water boils, the bubbles are full of steam, not air, by the way.

I could go on for hours. Ever notice how the pitch of the sound the spoon makes when it hits the side of the cup changes when you make instant coffee or cocoa? As the stuff dissolves, the "tink" gets lower. That's because the density of the liquid is increasing, and sound travels slower in a denser liquid. So what you're hearing is a kind of sonic red-shift.

Now, as long as we're on the subject, if you're interested in purchasing the complete Dr. Mabeuse Gourmet Cookware set for one hundred easy payments of $19.95, I'll also throw in a free copy of Cooking Like A Mad Scientist absolutely free!

--Zoot

 

[ABSTRUSE]

Thanks Zoot.
Lot of info there, I'm off to stare at a pot of boiling water now.

Do you take checks?
I'm really only interested in the cookbook.

 

[dr_mabeuse]

Thanks, Joe, for the reference to the Mpemba effect, but given the difficulty of teaching the kinetic theory of heat to freshmen, and getting them to understand the difference between heat and temperature, I wish I'd never heard of it.

And Abby, you can make that check payable to Bendover & Taykett, my holding company.

---Zoot

 

[English Lady]

Now I'm learning all kinds of interesting stuff (even if it hurts my brain trying to understand some of it )

Oh and I don't add salt to my water either....if someone wants salt they can add it themselves

And a cheque is on it's way Doc I want one of those cook books too!!!

 

[rgraham666]

My own two cents.

I was under the impression it was better to use cold water to make tea and coffee. The reason i had heard for this is that there are more gases, especially oxygen in the cold water, and this extra oxygen helps the processes that create the tea and coffee.

As far as Paradox goes, I still can't get past the big one. If human beings can think, why don't they?

 

[RebeccaLeah]

Altitude.

Boulder Colorado baby, screws up boiling water constantly. *sigh*