Under what conditions is the freezing of water as likely as the melting of ice?

Question

Caleb Adams · Accepted Answer

Same compound/purity. Otherwise, always.

The is a little confusing, because when pure water freezes, the temperature is the same for the melting of pure ice, #0^oC# or #32^oF#. Note I said pure. If contaminated water is subjected to cold, then the temperature of freezing is much lower than pure water. That said, the same contaminated water becomes ice, and its melting point is the same. If the substance is contaminated in one, and not the other, the melting and freezing points will differ. Hope this helps :)

Caleb Adams · Answer

The freezing of water is as likely as the melting of ice at 0 °C.

At 0 °C, water and ice are in a dynamic equilibrium.

Two things are happening:

Molecules on the surface of the ice escape into the water (melting)
Molecules of water are captured on the surface of the ice (freezing).
The rate of freezing is the same as the rate of melting, so the freezing is as likely as the melting.

Here's an animation of the freezing/melting equilibrium.

Ellie Andrews · Answer

undefined At the melting point of water, which is 0 degrees Celsius (32 degrees Fahrenheit) at standard atmospheric pressure, where ice and water are in equilibrium and can change from solid to liquid states, freezing and melting of water are equally likely.