Given:
The balanced chemical reaction of the synthesis of phosphorus trichloride:
2P + 3Cl2 ===> 2PCl3
Initial amount of phosphorus = 15 grams
The amount of product produced from 15 grams of phosphorus:
15 grams / 31 g/mol * (2/2) = 66.46 grams PCl3
The amount of chlorine is 44.31 grams, nearest to 45 grams.