If you are guided by your common sense, you will err. Neither will freeze at the same time nor will the 50ºC first: the first to freeze will be the hottest. This is the Mpemba effect , in honor of the young Tanzanian who discovered it while making ice cream in 1969.
It all has to do with supercooling : sometimes water does not solidify at 0ºC and remains liquid even at –20ºC. In these strange conditions , when freezing occurs, it occurs at a much higher speed than normal.
Hot water is more prone to supercooling for a curious reason: the hotter it is, the fewer gas bubbles it contains. And what does this have to do with freezing? Well, the bubbles act as "handles" so that the water molecules begin to orient themselves and form the crystalline structure of ice. The fewer "handles" the water has, the easier it is for it to stay liquid below freezing.
It must also be taken into account that ice floats in liquid water: a frozen lake is at the top, and the ice layer grows towards the bottom. This layer insulates the rest of the water from the cold air, causing it to freeze more slowly. However, in the case of supercooled water, as everything is at a temperature below zero, when the freezing begins it occurs suddenly , thereby winning the game over the mass of water that turns into ice along the way. normal.
