Use the standard reaction enthalpies given below to determine Δ_rH° for the following reaction: P₄(g) + 10Cl₂(g) → 4PCl₅(s) Δ_rH°= ?
Given:
PCl₅(s) → PCl₃(g) + Cl₂(g) Δ_rH°= +157 kJ
P₄(g) + 6Cl₂(g) → 4PCl₃(g) Δ_rH° = -1207 kJ

Question

Quizplus · Accepted Answer

To find Δ_rH° for the reaction P₄(g) + 10Cl₂(g) → 4PCl₅(s), use Hess's Law. Reverse the first reaction and multiply by 4: 4(PCl₃(g) + Cl₂(g) → PCl₅(s)) gives Δ_rH° = -4(157 kJ) = -628 kJ. Add this to the second reaction: P₄(g) + 6Cl₂(g) → 4PCl₃(g) with Δ_rH° = -1207 kJ. The total Δ_rH° is -628 kJ + (-1207 kJ) = -1835 kJ.

Use the Standard Reaction Enthalpies Given Below to Determine ΔrH°

Use the Standard Reaction Enthalpies Given Below to Determine Δ_rH°