How do you explain why puddles evaporate on cold days ?

Temperature is a measure of the average kinetic energy of an object. We can approximate this average kinetic energy using the relationship E≈kT. Where k is the boltzmann constant and T is the absolute temperature in Kelvin. Our water on the cold day (at 15°C) will then have an average energy of 4x10^(-21) J. The energy required for a single molecule of water to break the bonds to it neighbours is about 7x10^(-20) J which is much higher than the average so it would seem that water cannot evaporate. However water molecules actually have a range of energies. Some get 'lucky' and are involved in collisions that raise their energy and some will lose that energy. This range of energies is described by the Maxwell-boltzmann distribution. We can use the Boltzmann factor to approximate the ratio of molecules with enough energy to escape to the total number f=e^(E/(kT)) where E is the required energy, If we plug in our numbers we get that 7x10(-8) of the water molecules can evaporate. This look like a tiny amount but remember that in 1 liter of water there are 3x10^(25) molecules. So this evaporation is quite significant.