Question

Elemental phosphorus reacts with chlorine gas according to the equation: P4(s)+6Cl2(g)→4PCl3(l) A reaction mixture initially contains 45.21 g P4 and 130.4 g Cl2.

Part A Once the reaction has occurred as completely as possible, what mass (in g) of the excess reactant remains?

Express your answer to three significant figures.

m =

Answer 1

number of moles of P4 = 45.21g / 123.90 g.mol^-1 = 0.365 mole

number of moles of Cl2 = 130.4g / 70.9060 g.mol^-1 = 1.84 mole

from the balanced equation we can say that

1 mole of P4 requires 6 mole of Cl2 so

0.365 mole of P4 will require

= 0.365 mole of P4*(6 mole of Cl2 /1 mole of P4)

= 2.19 mole of Cl2

but we have 1.84 mole of Cl2 so Cl2 is limiting reactant

P4 is excess reactant

6 mole of Cl2 requires 1 mole of P4 so

1.84 mole of Cl2 will require 0.307 mole of P4

The number of moles of excess reactant = 0.365 - 0.307 = 0.058 mole

mass of excess reactant = 0.058 * 123.90 = 7.19g