Using average bond enthalpies (linked above), estimate the enthalpy change for the following reaction: H2(g) + F2(g)2HF(g)?

Refer to the values of average bond enthalpies.
The values of average bond enthalpies from difference sources may be slight different. This causes the result to vary slightly.

Equation for the reaction can be written as :
H-H(g) + F-F(g) → 2H-F(g) …… ΔH

Energy needed for bond breaking
= (436 + 155) kJ
= 591 kJ

Energy released in bond formation
= 567 × 2 kJ
= 1134 kJ

ΔH
= (Energy needed for bond breaking) - (Energy released in bond formation)
= (591 - 1134) kJ
= -543 kJ