Question

Why does evaporation causes cooling and why is water used in hot water bottles?

Answer 1

The specific latent heat of vaporization of water is 2260 J/g = 538 calories/g. Thus when water evaporates it absorbs large amount of latent heat and thus cooling is caused. The specific heat capacity of water is 4.2 J/kg°C = 1 cal/g°C which is quite high and this is the reason for using wafer in hot water bottles.