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–Cl
H–Cl
427
427

Cl–Cl
Cl–Cl
242
242

H–H
H–H
435
435

Hydrogen and chlorine gases react to produce hydrochloric acid according to the reaction.

H2+Cl2→2HCl
H
2
+
Cl

Answer 1

Use bond energies: break H–H (435 kJ) and Cl–Cl (242 kJ); form 2 H–Cl (2 × 427 kJ).

Energy required to break bonds = 435 + 242 = 677 kJ
Energy released forming bonds = 2 × 427 = 854 kJ

ΔH ≈ bonds broken − bonds formed = 677 − 854 = −177 kJ

The reaction is exothermic, releasing about 177 kJ per mole of reaction (≈88.5 kJ per mole HCl).