Suppose I would like to create a one molar solution of NaCl in water. The molar concentration is defined as
$n_i=1$ in this case. I need to take 58.5 grams of NaCl (atomic weight of Na=23 & Cl=35.5) and dissolve it in water until the total solvent volume is 1 litre. The total volume of the water added is less than 1 litre. But what exactly is that amount of water and how can I determine it apriori from thermodynamics?