Question

When PCl₅ is heated it gasifies and dissociates into PCl₃ and Cl₂. The vapour density of the gas mixture at 200ºC and 250ºC is 70.2 and 57.9 respectively. Find the percentage dissociation of PCl₅ at 200ºC and 250ºC.

Answer 1

If no dissociation were to occur,

It is important to note that the above relation between degree of dissociation and densities is applicable only when the reaction is accompanied by change in total number of moles. This relation is not applicable to reactions in which number of moles of the reactants and products are equal as in the formation or decomposition of HI.

H₂ + I₂ ⇄ 2HI