water freezing and its complications

[cresol]

It all started when I bet with my senior brother, that my warm tea will freeze before his, but instead his cold tea froze first....I felt bad so I tried it on my own with warm and cold water yet still the cold water freezes late. I was wondering why warm water freezes faster than cold water.....because with what I knw, cold water is likely to drop in temperature than hot or warm water. Please can any chemist open my eyes on this?

Thanks.

[ajb]

This is the Mpemba effect . I don't think there is a completely understood and agreed upon mechanism here.

The Royal Society of Chemistry organized a competition last year asking for mechanisms and the winner was Nikola Bregovic. You can find his paper here

[Washing machine]

I think that when water is heated it expands . And we all are aware that ice has more volume than water . So as the cold water freezes it expands to turn into ice which takes time . As the hot water is already expanded it takes less time to form ice because the expansion of the hot water has occurred which makes it consume less time to form ice and expand . As soon as the hot water freezes If we check the temperature of the hot water ice it would be HIGHER than that of cold water which has not formed ice yet . Therefore hot water freezes faster than cold water because hot water is already expanded while the cold water needs time to expand . It is all about expansion of water . Well thats what i think and it is just my opinion about what i think . I may be wrong or i may be right .

[hypervalent_iodine]

I think that when water is heated it expands . And we all are aware that ice has more volume than water . So as the cold water freezes it expands to turn into ice which takes time . As the hot water is already expanded it takes less time to form ice because the expansion of the hot water has occurred which makes it consume less time to form ice and expand . As soon as the hot water freezes If we check the temperature of the hot water ice it would be HIGHER than that of cold water which has not formed ice yet . Therefore hot water freezes faster than cold water because hot water is already expanded while the cold water needs time to expand . It is all about expansion of water . Well thats what i think and it is just my opinion about what i think . I may be wrong or i may be right .

!

Moderator Note

We ask that members not use mere opinion to answer genuine scientific questions. You should look at the link ajb posted. This has a good explanation.

 

Do not respond to this mod note within the thread.

[Bender]

I think that when water is heated it expands . And we all are aware that ice has more volume than water . So as the cold water freezes it expands to turn into ice which takes time . As the hot water is already expanded it takes less time to form ice because the expansion of the hot water has occurred which makes it consume less time to form ice and expand . As soon as the hot water freezes If we check the temperature of the hot water ice it would be HIGHER than that of cold water which has not formed ice yet . Therefore hot water freezes faster than cold water because hot water is already expanded while the cold water needs time to expand . It is all about expansion of water . Well thats what i think and it is just my opinion about what i think . I may be wrong or i may be right .

Let me break down where you got it wrong:

 

1) the expansion or contraction goes much, much faster than cooling

2) the hot water will first contract as it cools to 4°C before it can start expanding again. It cannot simply skip that

3) ice will not have a higher temperature than liquid water at the same pressure. It is possible that the liquid water is supercooled, but in that case, it is already below freezing temperature and only needs a slight nudge to freeze. (one of the hypotheses I have seen concerning the Mpemba effect involves the hot water getting supercooled, so that would be the reverse of what you suggest)

Edited May 10, 2017 by Bender