Question

Use the standard reaction enthalpies given below to determine H°rxn for the following reaction:

P₄ (g) + 10 Cl₂ (g) --> 4 PCl₅ (s)   ΔH_reaction = ?

Given:

PCl₅ (s) --> PCl₃ (g) + Cl₂ (g)   ΔH_{reaction = +157 kJ}

P₄ (g) + 6 Cl₂ (g) --> 4 PCl₃ (g)   ΔH_{reaction = -1207 kJ}

Choices:

A. -1835 kJ

B. -1364 kJ

C. -1050 kJ

D. -1786 kJ

E. -2100 kJ

Answer 1

PCl₅ (s) --> PCl₃ (g) + Cl₂ (g)   ΔH_{reaction = +157 kJ}

PCl₃ (g) + Cl₂ (g)   -->   PCl₅ (s) ΔH_{reaction = -157 kJ}

4PCl₃ (g) + 4Cl₂ (g)   --> 4PCl₅ (s) ΔH_{reaction = - 4*157 kJ} =-628 kJ

P₄ (g) + 6 Cl₂ (g) --> 4 PCl₃ (g)   ΔH_{reaction = -1207 kJ}

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P₄ (g) + 10 Cl₂ (g) --> 4 PCl₅ (s)   ΔH_reaction =-628-1207=-1835 kJ

ANSWER : A