Water molecules are bound together in a liquid by hydrogen bonds. Thus, in order for a single molecule to evaporate, it must have enough energy to break the hydrogen bonds with all of its neighboring molecules and then leave the liquid. This molecule had to have gotten this energy from the rest of the liquid, so each molecule that evaporates removes the same amount of internal energy from the remaining liquid. This loss of energy is called the heat of vaporization, and for water it is 40660 J/mol. Required:
Determine the amount of internal energy the hot drink initially has.