Enthalpy change for the reaction, 4H(g) 2H2(g) is -869.6 kJ The dissociation energy of H-H bond is
- -434.8 kJ
- -869.6 kJ
- +434.8 kJ
- +217.4 kJ
Answer
(3) +434.8 kJ
Solution
Formation of 2 mol H–H bonds: 4H(g) 2H2(g); H = -869.6 kJ
reverse (dissociation): 2H2(g) 4H(g); H = +869.6 kJ
for 1 mol: H2(g) 2H(g); H = +869.62 = +434.8 kJ
Bond dissociation energy is always positive (energy is absorbed to break a bond).
Answer: (3)