Cold water doesn't freeze faster/hot water doesn't boil faster

[MichaelD]

Somehow got into this coversation last night w/a coworker. I say that if you put hot water into a pot on the stove, it will boil faster than room temp water in the same pot/same flame. Reverse is true for cold water.

This just makes sense to me. Water freezes at 32F/0C. If you start out w/water at 50F, won't it freeze faster ( on the stopwatch ) than water starting at 75F?

 

[lokiju]

What leads you to think it wouldn't then?

Was your coworker saying this wasn't true or something?

I don't logically see how this couldn't be true.

 

[dighn]

you are right. if you coworker says otherwise ignore him/her.

 

[her209]

Yes, the water freezes!

 

[MichaelD]

Originally posted by: lokiju
What leads you to think it wouldn't then?

Was your coworker saying this wasn't true or something?

I don't logically see how this couldn't be true.

I've heard the contrary before in the past. To me, it's simple; if water is cold to begin with, it'll freeze faster. If it's hot to begin with, it'll boil faster. I seem to remember hearing/reading the contrary. Plus the annoying coworker...I just would like to know the real deal since I'm out of laboratory grade test equipment these days.

 

[HamburgerBoy]

lol, this reminds me of that one Hell's Kitchen episode.

 

[BigToque]

Whenever I make pasta, I put in hot water from the tap insead of room temperature. It seems logical that it would reach boiling/freezing point quicker since it's already at a higher/lower temperature to begin with.

Now the question for me is, what costs more money... running the tap unil the water is hot then bringing it to a boil, or putting room temperature water on the stove and letting the element run for a longer period of time to bring the water to a boil.

 

[Squisher]

Hot water can freeze faster than cold.

 

[BrownTown]

scalding hot water freezes faster than luke warm water, dunno about the other way around.

 

[Sphexi]

Easy to test. Take a cup of water and put it in the fridge for a few hours. Then take a cup of water and nuke it in the microwave until it's really hot. Put both in the freezer, check every hour or so, one will eventually freeze faster than the other.

 

[dighn]

Originally posted by: Squisher
Hot water can freeze faster than cold.

real world.. bleh, always complicates theory

very interesting though

 

[Evadman]

warm water will heat and boil faster than cold, but hot water will freeze faster than cold.

 

[MichaelD]

Originally posted by: Evadman
warm water will heat and boil faster than cold, but hot water will freeze faster than cold.

Head goes --> *BOOM*

I like the responses/links; keeps me thinking. It's not a "black and white" question, apparently/unfortunately!

 

[Fritzo]

Don't make fun of him...I got learned the same thing in college

Really...it has something to do with dissolved gas in cold water and it's molecular alignment.

::Edit:: Oops...someone already posted a link. Neat though

 

[SoulAssassin]

Hot tap water has more air in it than room temp tap water, therefore it takes longer to boil.

 

[imported_Imp]

Isn't it all about how many joules of energy you need to raise the temperature? Like you need to get it to 10J before boiling, but if it's already at 4, you only need to add 6, etc. For the love of God, don't quote me on those values.

 

[DaiShan]

Originally posted by: MichaelD
Somehow got into this coversation last night w/a coworker. I say that if you put hot water into a pot on the stove, it will boil faster than room temp water in the same pot/same flame. Reverse is true for cold water.

This just makes sense to me. Water freezes at 32F/0C. If you start out w/water at 50F, won't it freeze faster ( on the stopwatch ) than water starting at 75F?

When someone says putting cold water in a pot will boil faster than putting hot water in the pot they are correct if you look at it this way: It takes longer for the water to get hot at the tap then put it into the pot and boil it than it does to just put cold water in the pot in the first place. For example, say water is coming out of your tap at 75 degrees F. Your hot water heater probably only puts out water at 120 degress F max. This might take several minutes to reach, whereas if you put the room temperature water in the pot on the flame it will heat much faster than the heating elements in your water heater. The cold water argument in my opinion is faulty. Anyone care to test?

 

[mugs]

Google Mpemba Effect

Edit: I did it for you:
http://en.wikipedia.org/wiki/Mpemba_effect

 

[91TTZ]

Originally posted by: MichaelD
Somehow got into this coversation last night w/a coworker. I say that if you put hot water into a pot on the stove, it will boil faster than room temp water in the same pot/same flame. Reverse is true for cold water.

This just makes sense to me. Water freezes at 32F/0C. If you start out w/water at 50F, won't it freeze faster ( on the stopwatch ) than water starting at 75F?

You are correct. The others are wrong.

The people who claim otherwise point to studies that claim that, "in some specific circumstances", hot water can freeze faster than cold water. It's the exception, and not the rule.

 

[Kyle]

high school chem class- we took one beaker of cold water and one beaker of hot water- put them both over a bunsen burner and the cold water boiled before the hot water. I dont remember his explanation (I hated chem) but that experiment always stood out for me.

*edit*
after some googling it seems it is a myth, but I really dont know why it worked in our lab though...cause no one believed our teacher so he told us to prove him wrong and we couldnt...

 

[MichaelD]

DaiShan has a point about the hot water heater heating the "base water" from it's start temp to "whatever temp" first...and adding "preheating time + heating time."

But that's not what I'm talking about. I'm talking about:

1. Take two equal heating elements (forget preheat times or whatever, they don't count!)
2. Add to each cold water at 0C and cold water at 32C.
3. Which one will boil faster? I say the water that started at 32C!

 

[Evadman]

Originally posted by: Imp
Isn't it all about how many joules of energy you need to raise the temperature? Like you need to get it to 10J before boiling, but if it's already at 4, you only need to add 6, etc. For the love of God, don't quote me on those values.

1 joule will raise the temp of one mm^3 of water 1 degree. so for your example, if you had 1 mm^3 of water at 94C you would need 6 more joules to boil it in a perfect world. however, the world is not perfect

 

[Tiamat]

n/m

For pure water in a uniformly mixed container, the cold water will freeze faster than the hot water.

 

[RaynorWolfcastle]

Cool water may not freeze as fast as hot water in some situations. For example, hot water is used in Zambonis when resurfacing ice because it freezes faster than warm water. The reason is supposedly that the hot water has lower viscosity than cool water, so it spreads out better and doesn't make puddles as cool water would .

 

[91TTZ]

Originally posted by: RaynorWolfcastle
For example, hot water is used in Zambonis when resurfacing ice because it freezes faster than warm water. .

They use hot water because it melts the ice more, resulting in a smoother surface.