Write the equation for the dissociation of HF into H and F atoms. Classify the reaction as endothermic or exothermic, and give the AH value for the reaction.

Question

Note: Reference the Bond energies table for additional information.

kcal
mol

Bond

H-H

F-F

C1-C1

Br-Br

I-I

H-OH

H-F

H-C1

H-Br

H-I

energy

+104

+38

+58

+46

+36

+119

+136

+103

+87

+71

Answer 1

The equation for the dissociation of HF into H and F atoms is:

2 HF (g) -> H2 (g) + F2 (g)

This reaction is endothermic as energy is required to break the bonds of HF and form H2 and F2. The AH value for the reaction can be calculated using bond energies.

AH = (2 * AH(H-F)) - (AH(H-H) + AH(F-F))
AH = (2 * 136) - (104 + 38)
AH = 272 - 142
AH = 130 kcal/mol

Therefore, the AH value for the dissociation of HF into H and F atoms is +130 kcal/mol.