Calculate percentage change in Mavg of the mixture, if PCl5 undergo 50% decomposition. PCl5 ⇌ PCl3 + Cl2

Engineering

Chemistry

Degree of Dissociation and Equilibria

Determination of Atomic and Molecular Mass

Question

Calculate percentage change in M_avg of the mixture, if PCl₅ undergo 50% decomposition.
PCl₅ ⇌ PCl₃ + Cl₂

33.33 %

50 %

66.66 %

Zero

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Take initial mole of PCl₅ = 1
  PCl5 → PCl₃ + Cl₂
initial moles   1   –   –
final moles   0.5   0.5   0.5
M_initially = M_w of PCl₅ = 208.5 g
${\bar{M}}_{finally} = \frac{208 .5}{1 .5} = \frac{total mass}{total moles}$
= $\frac{2}{3}$ × 208.5
$change in \bar{M} = 208 .5 - \frac{2}{3} \times 208 .5 = \frac{1}{3} - 208 .5$
   % change = $\frac{\frac{1}{3} \times 208.5}{208.5} \times 100$ = 33.33 %