Question

Elemental phosphorus reacts with chlorine gas according to the equation:
P4(s)+6Cl2(g)→4PCl3(l)
A reaction mixture initially contains 45.83 g P4 and 130.2 g Cl2.

QUESTION: Once the reaction has occurred as completely as possible, what mass (in g) of the excess reactant is left?

Answer 1

P4    +    6 Cl2 -----------------------> 4 PCl3

124g          426 g                                   550 g

45.83g       130.2g

first calculate limiting reagent

124 g P4 ----------------------> 426 g Cl2

45.83 g P4 --------------------> ???
Cl2 needed = 45.83 x 426 / 124

                     = 157.4 g Cl2 needed for this reaction

but we have only 130.2 g Cl2 is present . so Cl2 is limiting reagent

now :

P4 reacted = 124 x 130.2 / 426

                     = 37.90 g

remaining = 45.83 - 37.90

                 = 7.93 g

excess reactant is left = 7.93 g