Deduce the equilibrium constant expression, K_c, for the decomposition of PCl₅(g).

Deduce, giving a reason, the factor responsible for establishing the new equilibrium after 14 minutes.

Deduce the Lewis (electron dot) structure and molecular geometry of PCl₃.

«K_c» = \(\frac{{\left[ {{\text{PC}}{{\text{l}}_3}} \right]\left[ {{\text{C}}{{\text{l}}_2}} \right]}}{{\left[ {{\text{PC}}{{\text{l}}_5}} \right]}}\)

[1 mark]

decrease in temperature

endothermic «reaction» AND «equilibrium» shifts to the left/reactants
OR
endothermic «reaction» AND K_c decreases
OR
endothermic «reaction» AND concentration of PCl₅ increased/concentration of PCl₃ and Cl₂ decreased
OR
«equilibrium» shifts in exothermic direction

Do not accept “temperature change”.

Accept “ΔH positive” in place of “endothermic”.

Accept “products” instead of “PCl₃ and Cl₂”.

[2 marks]

Lewis structure:

Molecular geometry:

trigonal/triangular pyramidal

Penalize missing lone pairs once only between this question and 4(b).

Accept any combination of lines, dots or crosses to represent electrons.

Do not apply ECF.

[2 marks]