Question

SO₃​(g) is heated in a closed vessel. An equilibrium 2SO₃​(g) ⇌ 2SO₂​(g) + O₂​(g)
is established. The vapour density of the mixture, in which SO₃​ is 50% dissociated, is:

(a) 32

(b) 35

(c) 42

(d) 55

Answer 1

Correct option is (a) 32

SO₃​(g) is heated in a closed vessel. An equilibrium 2SO₃​(g) ⇌ 2SO₂​(g) + O₂​(g) is established. 

Sulfur trioxide has molar mass of 80 g/mol. It's vapour density (before dissociation) is 

D = \(\frac{80}2\)​ = 40

2 molecules of SO₃​ on dissociation gives 3 molecules of gaseous products.

1 molecule of SO₃ on dissociation gives \(\frac 32\)​ = 1.5 molecules of gaseous products.

n = 1.5

The vapour density of the mixture, in which SO_3​ is 50% dissociated, is 32.