Question

Use the information in the table to answer the question.

Bond Between Atoms and Their Respective Electronegativity
Bond Bond Energy ( kJ/mol
kJ
/
mol
)
H-I
H-I
297
297

H-H
H-H
435
435

I-I
I-I
151
151

Hydrogen and iodine gases react to produce hydroiodic acid according to the reaction.

H2+I2→2HI
H
2
+
I

Answer 1

Calculate ΔH using bond energies: bonds broken − bonds formed.

Bonds broken: 1 H–H + 1 I–I = 435 + 151 = 586 kJ
Bonds formed: 2 H–I = 2 × 297 = 594 kJ

ΔH = 586 − 594 = −8 kJ

The reaction is exothermic by 8 kJ per mole of H2 (ΔH ≈ −8 kJ).