a) Water has a molar mass of 18 g/mol and a density of 1000 kg/m3 (or 1 g/cm3). Based on this data, estimate the number of water molecules per unit surface area of water.
b) The coordination number of water (i.e., the average number of "neighbors" each water molecule has) in the liquid state is 4. Neighboring water molecules attract each other via hydrogen bonds, each of which has a binding energy of roughly 10–20 J (although this number depends relatively strongly on temperature). Use this information to estimate the surface tension of water. How does your estimate compare to the observed figure (
γ water = 0.072 N/m ) (hints: Keep in mind that we can think of
surface tension as surface energy per unit area, and consider the energy needed to bring a molecule from the bulk to the surface)?
