If hot water freezes faster, then does cold water boil faster?

Question

Our plumber hooked up the hot water to my ice maker, saying that many people think it freezes faster because of how much energy it takes to get water temperature moving. Once it gets moving in the right direction, it can move faster and faster. Have ya heard this? Okay, so does cold water boil faster? Just wondering.....

Answer 1

Hot water *can* freeze faster than cold water, but in most cases will not. The phenomenon is called the Mpemba effect. There is no settled theory to explain it, but some people think it's because of air currents forming over the hot water. It only works under certain conditions, so counting on it to work in your ice maker is probably a bad idea.

There is no comparable effect with boiling water; it takes more time and energy to boil cold water because you have to heat it more.

Answer 2

Your plumber is a chemistry moron.

In order for water to freeze, the molecules need to move slower, not faster. A solid is the phase of matter where the molecules have so little energy that they only vibrate in place.

The average temperature of the water, in order for it to freeze, must be 32°F or 0°C. It obviously takes less energy loss for something to go from 20°C (room temperature) to 0°C than from 35°C (about the temperature of a warm shower) to 0°C.

So, unlike what your plumber told you, cold water freezes faster than warm water.

Easy test: Place an ice tray full of cold water and another ice tray full of hot water into two seperate freezers (they have to seperate or heat exchange will occur between the two ice trays). Check them at intervals of time. I guarantee the cold water tray will turn to ice before the warm water tray does.

Answer 3

a given volume of Hot water will freeze faster than the same volume of cold water because hot water cools in the icebox and cools itself by evaporation. You'll make more ice from the cold water, but if time is a factor, make a little less ice with hot water faster. Going the other way won't work, Unless you can heat the cold water and magically make the water heat itself as well.

Answer 4

Cold water freezes faster because it has less heat to give up than hot water. Similarly, hot water boils faster because it needs to take in less heat to reach boiling point. Try this on a stove with equal volumes.

Answer 5

No. It takes a lot of calories to heat water degree by degree. One calorie is the amount of heat needed to raise one cubic centimeter of water by one degree Celsius. So, with equal water mass, the warmer water has a head start versus the colder water.

There is a totally different dynamic when it comes to freezing in the sense that the plumber is talking about. At our house in winter, when the wind blows and the temperature dips below zero, the hot water lines will indeed freeze before the cold water lines. What's at work here is the ambient temperature, which is below zero, and the principle of diffusion of heat until it is evenly distributed. So I have an ambient temperature (outside the pipes), a cold water line temperature (inside that pipe), and a hot water temperature (inside that pipe). If the water remains motionless (nobody turns on the faucet to let the water run), the hot water line temperature will drop really fast because nature likes an even distribution (like water finding its own level) of heat. The temperatures are going to trend toward the ambient temperature, the hot water line temperature, and the cold water line temperature, all being equal. The cold water line doesn't give off nearly as much heat to the ambient air. The hot water sends a lot of heat into the ambient air. The ambient air molecules around the hot water line are vibrating much faster, diffusing into the rest of the ambient air faster than the slower vibrating ambient air molecules around the cold water line. This faster vibration is what causes the hot water line to give up its heat to match the ambient air temperature faster than the slower vibration from the cold water line. Eventually, the 3 temperatures will all be equal and both water lines will be frozen, but the cold water line held on to its heat longer because the molecules weren't moving as fast and giving up heat as fast.

Similarly, if I want to heat a room to 70 degrees Fahrenheit in the wintertime using water running through pipes, I depend on hot water giving up a lot of its heat in order to heat the ambient air in the room. The ambient air molecules near a pipe with water heated to 180 degrees F will vibrate, rotate, and translate much faster and diffuse the heat through the room much faster than than if I were to send 70 degrees F water through the pipe. When the 180 degree water reaches the furnace to be reheated, it cooled off a whole lot, while the 70 degree water will not have dropped much temperature at all by the time it reaches the furnace for reheating. So the hotter water gives up a lot of its heat to the ambient air and the cooler water keeps much of its heat, and gives little of it to the ambient air.

When applying heat to make water boil, both the cold and the hot water are being heated up to a point much higher than the ambient air, so the ambient air is trying to cool the water down while the flame is trying to push the water temp much higher than the ambient air. It's similar to walking with the wind and walking against the wind. With cold ambient air, it helps freeze water (walking with the wind), but doesn't help heat it (walking against the wind) so the cold water has many more degrees to heat (a longer distance to walk against the wind) to reach boiling than the hot water does.

Answer 6

it's a common misconception that people have that hot water boils faster than cold water. This is untrue cold water DOES boil faster than hot water.

Answer 7

no it's not true,, cold water freezes faster,,, i have tested this.
change it back to cold,, it will save you energy.

Answer 8

It just doesn't make any sense. It defies all logic why someone would thing that it would freeze faster.