为什么热水比冷水结冰快？

We demonstrate that the Mpemba paradox arises intrinsically from the release rate of energy initially stored in the covalent H-O part of the O:H-O bond in water albeit experimental conditions. Generally, heating raises the energy of a substance by lengthening and softening all bonds involved. However, the O:H nonbond in water follows actively the general rule of thermal expansion and drives the H-O covalent bond to relax oppositely in length and energy because of the inter-electron-electron pair coupling [J Phys Chem Lett 4, 2565 (2013); ibid 4, 3238 (2013)]. Heating stores energy into the H-O bond by shortening and stiffening it. Cooling the water as the source in a refrigerator as a drain, the H-O bond releases its energy at a rate that depends exponentially on the initially storage of energy, and therefore, Mpemba effect happens. This effect is formulated in terms of the relaxation time tau to represent all possible processes of energy loss. Consistency between predictions and measurements revealed that the tau drops exponentially intrinsically with the initial temperature of the water being cooled.我们说明了 Mpemba 悖论的产生原因：它是由于在水的氢键状态(O:H-O)下，氢氧共价键(H-O)释放能量的速度在不同实验条件下是不一样的。一般来说，将一个物体加热，这个物体内的所有化学键都会增长且变得更加灵活。然而，水中的氢键(O:H)在遵从这个规律的情况下，将氢氧共价键推向了相反的方向，也就是说温度越高，氢氧共价键反而更短更不容易变形；这是由于氢键和共价键直接的电子相互作用[J Phys Chem Lett 4, 2565 (2013); ibid 4, 3238 (2013)]. 因而，氢氧共价键在储存能量的情况下变得更短而结实。当水在冰箱中冷却时，氢氧共价键释放热量的速率与其最初储存的能量呈指数关系（译者注：指数关系表明了热水释放热量的速率会明显大于冷水），所以 Mpemba 效应就会发生。文章中，我们用弛豫时间来定量计算了能量释放的过程；实验和我们预测的指数关系是相互符合的。