text: I don't have a calculator handy, but I'll help where I can.\n\nEvaporation is endothermic, meaning that it takes in heat.  The amount of heat taken in when one mole of water evaporates is its molar enthalpy of vaporization.\n\nSo, first, find out how much of the water evaporated.  Assuming standard conditions, 1 mL of water weighs 1g.  So that means that 16g of water evaporated. (With me so far?)  Now use that to find out that you have a bit less than on mole of water vapor.\n\nWhere did the energy that the evaporating water use come from?  The other molecules of water.  You know that the amount of energy released when 284g of water decreases temperature is related in the formula q=mC(Tfinal-Tinitial).  (Only the other 284g of water decreased temp...the other 16g gained temp.)  Now you can figure out how much energy the water vapor absorbed when it changed into a gas.\n\nTake the energy # and divide by the # of moles... and you are set.\n\n\nOh side note: since you are dropping the pressure, you do not need to worry about heating the water up inorder to make it boil.