Chapter 5, Problem 52PS

### Chemistry & Chemical Reactivity

10th Edition
John C. Kotz + 3 others
ISBN: 9781337399074

Chapter
Section

### Chemistry & Chemical Reactivity

10th Edition
John C. Kotz + 3 others
ISBN: 9781337399074
Textbook Problem

# You wish to know the enthalpy change for the formation of liquid PCl3 from the elements.P4(s) + 6 Cl2(g) → 4 PCl3(ℓ) ΔrH° = ?The enthalpy change for the formation of PC15 from the elements can be determined experimentally, as can the enthalpy change for the reaction of PCl3 (ℓ) with more chlorine to give PCl5(s):P4(s) + 10 Cl2(g) → 4 PCl5(s)ΔrH° = –1774.0 kJ/mol-rxnPCl3(ℓ) + Cl2(g) → PC15(s)ΔrH° = –123.8 kJ/mol-rxnUse these data to calculate the enthalpy change for the formation of 1.00 mol of PCl3(ℓ) from phosphorus and chlorine.

Interpretation Introduction

Interpretation:

The enthalpy change for the formation of 1mole of PCl3 has to be determined.

Concept Introduction:

If a reaction proceeds in two or more other reaction,ΔrH0 for the overall process is the sum of ΔrH0 values of those reactions-Hess’s law.

Explanation

The required equation for the formation of PCl3 is found out by multiplying the 2nd equation by 4

â€‚Â 4PCl3â€‰+4Cl2â€‰â†’â€‰4PCl5

Â And then by subtracting the 2nd equation from the 1st equation, so we get,

â€‚Â P4â€‰+â€‰6Cl2â€‰â†’â€‰4PCl3

â€‚Â Î”rH20=4Ã—-123.8kJ/mol =-495

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