Why Can Hot Water Freeze Before Cold Water?

The claim that hot water can freeze before cold water is commonly called the Mpemba effect. The important word is “can”. It does not mean hot water always freezes first, and it does not violate thermodynamics. It means that under some experimental conditions, water starting at a higher temperature may produce ice sooner.

Initial temperature is not the only variable. Evaporation can reduce the amount of water left to freeze. Temperature differences alter convection and heat transfer. Dissolved gases, the way the container contacts its surroundings, and the degree of supercooling can also affect the outcome. That is why the phenomenon is difficult to study: apparently minor experimental details can change which sample freezes first.

So “hot water always freezes first” is wrong, while “hot water can never freeze first” is too absolute. Recent experimental work still examines the definitions and conditions under which the effect can be reproduced. The real lesson is methodological. Scientific claims lose meaning when their conditions are stripped away. Counterintuitive results are often less mysterious than they appear; our intuition has simply left out variables.

https://royalsocietypublishing.org/rspa/article/476/2241/20190829/80766/Observing-the-Mpemba-effect-with-minimal-bias-and
https://pubs.rsc.org/en/content/articlelanding/2026/lf/d5lf00212h