Question

A 2.5 mol sample of phosphorus pentachloride, PCl5 dissociates at 160C and 1.00atm to give 0.338 mol of phosphorus trichloride at equilibrium. What is the composition of the final mixture?

Answer 1

Explanation:

Moles of phosphorus pentachloride present initially = 2.5 mol

Moles of phosphorus trichloride at equilibrium = 0.338 mol

$PCl_5\rightleftharpoons PCl_3+Cl_2$

Initially

2.5 mol      0    0

At equilibrium:

(2.5 - x) mol      x     x

So, from above, the moles of phosphorus trichloride at equilibrium , x= 0.338 mol

Mass of 0.338 moles of  phosphorus trichloride at equilibrium:

= 0.338 mol × 137.5 g/mol = 46.475 g

Moles of phosphorus pentachloride present at equilibrium :

= (2.5 - 0.338) mol = 2.162 mol

Mass of 2.162 moles of  phosphorus pentachloride at equilibrium:

= 2.162 mol × 208.5 g/mol = 450.777 g

Moles of chloride gas present at equilibrium : 0.338 mol

Mass of 0.338 moles of chloride gas at equilibrium:

= 0.338 mol × 71 g/mol = 23.998 g