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# Hot water is heavier than cold water, true or false?

Question #59964. Asked by trimtrivia. (Oct 13 05 11:22 PM)

picqero

Water, like most other materials, expands when heated so cold water is denser than hot water and is therefore heavier, assuming the quantities are identical of course. This is why the top of a water heated radiator warms up before the bottom; the warmer water 'floats' on top of the colder water. The same effect is sometimes very evident while swimming in a calm sea or lake, the warmer water being close to the surface.
Simply heating any quantity of water, however, will not increase or decrease its weight.

 Oct 14 05, 11:14 PM
dunnkeeh

Water in its normal state will decrease in density as you increase its temperature. Example, water at 4 degrees Celsius has a density of .99998 g/ml, and at 30 degrees Celsius has a density of 0.9957 g/ml. However there exists the possibility for water to be super cooled. In nature this usually only happens in clouds. But if you cooled it quick enough you could super cool it to -45 degrees Celsius before it froze. Water that is super cooled decreases in density the colder you get. Water that is -30 degrees has a density of 0.9839 g/ml.

 Feb 20 07, 3:36 PM
234cks234

Everybody below is off. It actually depends. If you have 2 liters of water and then you heat 1 liter one and make another one cold the hot water is actually heavier. Accoring to Einstein Energy has mass. E=mc2 Therefore when you add energy to something it actually gets heavier. Therefore Hot water is actually heavier than cold water. If you look at it this way, even though the cold water takes up less space as particles are closer together, and the hot water takes up more space, there are still the same amount of particles, and the particles weigh the same. However because you add energy, and energy has mass, the hot water will be slightly heavier.

 Dec 24 09, 1:42 PM
Baloo55th

Start from scratch. Take two separate litres of water and heat one. They will remain the same mass (= weight for most purposes down here on Earth). Now take a litre of water from the hot tap and compare the weight with a litre from GingeryNutt's water container on a Christmas campsite. The hot one weighs less because it's less dense. In the first example, the heated litre will actually expand over the one litre boundary. (In fact, GingeryNutt's water froze on the first night we were there...)

Mass can be converted to energy - and a minuscule amount of mass gives a vast amount of energy. It would take an amount of energy that would probably vaporise the water (and the experimenter) to make a difference to the mass of the water. Quote: "For example, when water is heated in a microwave oven, the oven adds about 1.11×10^−17 kg of mass for every joule of heat added to the water.". (I've inserted a ^ as the superscript -17 came through as normal -17.) That's not something you can measure on your kitchen scales, or even on your school science lab scales. 10 to the power 17 is 1 followed by 17 noughts. -17 makes it 0.000 000 000 000 000 001 (in this case 0.000 000 000 000 000 001 11 kg). The expansion of the water (and consequent reduction of density) will be a larger factor. http://en.wikipedia.org/wiki/E%3Dmc%C2%B2

 Dec 30 09, 6:47 PM
evil44

OK, first off, it depends on how cold the water is. As water is cooled toward freezing, it contracts, thereby taking up less space and thereby weighing more per volume that hot water. However, at 4°C, water begins to expand when further cooled, then greatly expanding once frozen. This priciple is what allows life on Earth to flourish. If frozen water were more dense than warmer water then lakes would end up freezing from the bottom up, thereby killing all life forms in them. The frozen layter at the top of the lake allows the more dense warmer water below to stay above freezing temperatures and life to continue.

http://www.bookrags.com/research/thermal-expansion-wop/

 Mar 25 10, 8:50 AM

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