at -5 celcius how long does it take water to freeze?

Answer 1

At -5 degrees a water molecule already froze. So technically water already froze at -5 degrees, it does not take any time.

-j-

Answer 2

It's really impossible to effectively model the freezing rate of water with an equation, given the numerous factors at play. Even if you knew all the properties of the water, only an experimental test can really tell you what you want.

That said, Fourier's Law can give you a rather rough approximation of what you want to know. Fourier's Law's intended use is for calculating rate of heat transfer through a substance but it can be applied here.

After some very rough calculations based on Fourier's Law, the time for the water to freeze should be (in seconds) 74 + 4.184*starting temperature of the water in celsius. This assumes a cubical container for the water.

The total energy loss needed to freeze the water is 334 J/ml at 0 celsius (the heat of fusion of water) + 4.184 J/(ml * degree celsius) to lower the temperature to 0 C. Based on Fourier's Law, it takes 74s to freeze the water at 0 C regardless of the volume (for a cube the variables eventually cancel). To get the water down to that takes 4.184 s per degree.

Answer 3

How much water? What is the starting temperature of the water? Is the water in an insulated container? Is the water still or is it agitated?

There are lots of other factors that need to be considered.

Answer 4

Depends how much water there is, its density, any other mixtures in there (e.g salt) and more.