Everyday science: Why does warm water freeze faster?

Updated: Oct 9, 2019

When exposed to room temperature Liquid Nitrogen forms a gas.

Have you ever noticed that warm #water freezes faster than #cold water? While there is no officially accepted answer, here’s my #theory.

We know water [H2O] is at its most #dense at 3.98c (@ 101.325 kPa sea level), that is, at this #temperature water molecules are in the closest proximity to each other in a specified space. The Hydrogren [H] bonds between them are stable and can only be weakened by #heating (>3.98c) the water and increasing the kinetic energy of the molecules causing them to vibrate away from each other (thermal expansion).

We know as water cools below 3.98c, water also becomes less dense as the molecules spread out, becoming perfectly aligned in order to create a #lattice (solid crystal) structure at freezing point 0c (@ 101.325 kPa sea level).

We also know as water warms above 3.98c the water becomes less dense as water molecules spread out through the process of thermal expansion and eventually break their Hydrogen [H] #bonds completely forming steam at 100c (@ 101.325 kPa sea level).

Typically warm water (>3.98c) is accepted to be about 40-50c so is therefore less dense than cold water (<3.98c). The molecules are further apart and the Hydrogen [H] bonds between them are less stable than in cold water (3.98c). Therefore it stands to reason that when cooled #rapidly, the #molecules should form an ordered lattice (solid crystal) quicker than in cold water due to the already existing space between them and the sudden removal in heat resulting in a reduction of kinetic energy.

A water molecule consist of 2 Hydrogen Atoms bonded to 1 Oxygen Atom via a covalent bond.

It’s similar to #desublimation and makes sense if we consider anything above 3.98c is approaching boiling point (100c). When chilled rapidly below freezing point (0c) it’s going to be quicker for the water to form a lattice #structure (solid crystal) if the Hydrogren [H] bonds between the molecules are already weak as opposed to cold water where the Hydrogen [H] #bonds are strong and more effort is required to form the lattice (solid crystal) structure.

Based on this premise, warm water (> 3.98c) is always going to freeze #quicker than cold water (< 3.98c) at 101.325 kPa sea level given it’s the shortest path to forming solid matter.

Nick Griffin

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