A bottle of iced water or a bottle of tap water? I would have thought the iced, but is that right?

You know how (apparently, I've not tested this myself) hot water freezes quicker than cold water? Well i wonder if this is the same? ie not what you would expect.

WTF?? Hot water freezes quicker than cold????!

WTF?? Hot water freezes quicker than cold????!
Under some limited circumstances, apparently yes.
http://en.wikipedia.org/wiki/Mpemba_effect

The iced water will have ice in it keeping it cool until its all melted.

If you had water at zero but no ice and water at 10 deg no ice they would both increase in temp at the same rate.

I have heard the hot water freezes faster thing from when I was a kid (making slides in the icy weather), would think that one is not quite right though maybe it is, I wasnt too bothered as long as I had a good slide.

The question needs bounding more.

Are you referring to rate of change of warmth (temperature) or how quickly does it take for both to reach a defined value?

When you say 'heat up quicker' do you mean degrees C per hour, or as a ratio (percentage) of its temperature or for both the iced and liquid water to reach a higher temperature under the same warming conditions?

Freezing depends on more than temperature, distilled water with no impurities can stay liquid down to very low temperatures. So boiled water may be easier to start the freezing process.

Ice requires the input of lots of heat (which becomes latent heat) in order to melt. That's why ice cools your gin & tonic when a lump of metal at the same temperature wouldn't work the same.

So water with ice in will stay colder than water on its own, assuming the ambient temperature is higher than zero.

As above – hot water will not freeze quicker than cold, but the rate of exchange is quicker if what I understand is correct.

the mpemba hypothesis suggests that a vessel of hot water placed in a freezer will quickly establish convection currents, these movements in the water prevent the surface from freezing over, the currents continue to flow, and the heat energy of the water is quickly conducted away to the air above the water and through the walls of the vessel.

a vessel of cold water will not develop the same convection currents, so the surface of the water can freeze over, acting as an insulating layer.

there has been a little research into this, and it seems there may be something in it, but conditions have to be 'just so'…

temperature gradient has a lot to do with the case described by billy; the cold water will increase in temperature at a faster rate, because there is a bigger difference driving the energy through the sides bottle, but i don't see why it should warm up to Xdegrees before the warmer water.

if there is ice in the bottle, then the temperature of the water will stay at zero until the ice has melted. latent heat and all that.

You are right.

They will both warm up at the same speed, however, the iced water will take longer to reach the ambient temperature as it was colder to start with.

my question refers to drink bottles on a bike. I'm in a hot country and I want to know if chilling my drinks before I ride is worth doing or not. It doesn't seem to help much!

BillyWhizz -hot water freezes quicker than cold water

a nasty rumour started by adults living on hills to stop kids (us) making ice slides down the footpath of said hill! we only fell for it once!

Depends how long the rides last!

the hot water freezing quick thing is an urban myth – it can happen under some pretty ludicrus lab conditions but even then the difference in rate of cooling is pretty small.

Easy way to think why it wouldn't happen – imagine a graph showing the temperature of the two vessels over time. basically this would be 2 lines sloping downwards to the right perhaps concave or convex – but definitely sloping to the right. If the hot water froze faster than the cold then at some points the lines would cross – at this point the two bodies of water would be at the same temperature – and under the same cooling conditions those two bodies could only possibly cool any further at the same rate – this shows that the best you could expect would be that the hot water would cool to a specific point at the same time as the cool water.

(yeah yeah i know that temperature within the vessel will vary…)

It's probably a corruption of the rate of cooling – so a vessel of boiling water might get to say 90' in a minute whereas a vessel of water at 10' might only get to 9.5' in a minute. Plus folk who make water slides using boiling water probably are not doing a control group with cold water – then when they miraculously get ice they jump to the conclusion that it was because they used boiling water.

Stop worrying about it and just chill your bottles as normal. Ignoring pretty small-scale convection currents, and being aware that your bottle is being bounced about left right and centre on teh bike and so has currents in it most of the time, the only difference is overall temperature rise. The colder bottle will absorb heat faster than the warmer bottle, larger temp difference so faster heat transfer, but since it started lower it takes longer to reach the same temp anyway. Even better if you can freeze the bottle, as the melting ice takes loads of energy, keeping your bottle cold longer. I spent a summer in cyprus with 2 litre bottles of water frozen solid overnight, they generally lasted 3-4 hours in 40+ C and direct sunlight.

billywhizz, i've been thinking about this for a good 45 seconds now and i've come up with two theories;

1: you're on half term from primary school and you've borrowed your moms pc while your xbox loads.

or

2: you're trolling.

or 3 – I'm in south africa on holiday, its 30+ degrees and I'm dying on the bike every afternoon. I can use tap water, water cooler water, or ice cubes in my bottles, but it seems whichever way I go, after the first 20km the drink is warm . . . . .

fair enough but common sense tells you that the cooler it starts the longer it'll stay cooler. anyway, you're on holiday, get off the internet. holiday rule 1; get hot, hit pool.

the pool & a cold beer is there for when I get back 🙂

Yuo're just out-riding your supply of cool I'm afraid. Get freezing.

Put the full bottles in the freezer overnight and freeze them solid. You'll be surprised how long they stay cool. If you can keep the bottles in the shade, even better.

Get a bloody camelbak. They are insulated.

Or failing that an insulated bottle.

Simples.

http://www.polarbottle.com/products/

I got a drinks bottle in the USA which was made of plastic and was bouble skiined, it had some kind of plastic fild between the two layers of plastic. It reduced capacity a bit but it did keep the drinks cooler for longer.

As above best to freeze your bottle overnight or fill up with ice cubes, tap water will get to ambient quicker simply because it is warmer to start with. IIRC The specific heat of water is a calorie (4.2 joules) per millilitre per degrees centrigrade whether its at 1 deg C or 90 deg C. Wether its been boiled before or not makes no difference, the only difference is that the water will have been largely degassed by the boiling process.

The ice will require latent heat to melt.
The tap water will reach ambient temp before the iced water.