Enthalpy Change and Dissociation Energy Calculation

Enthalpy Change Calculation:
- The given reaction is 4H(g) ----> 2H2(g)
- The enthalpy change for this reaction is -869.6 kJ
- This means that the reaction is exothermic, and 869.6 kJ of energy is released when 4 moles of hydrogen gas react to form 2 moles of hydrogen gas.

Dissociation Energy Calculation:
- The dissociation energy of the H-H bond can be calculated using the enthalpy change of the given reaction.
- Since the given reaction involves the formation of H2 from H atoms, we can assume that the bond dissociation enthalpy of the H-H bond is equal to the enthalpy change of the given reaction divided by the number of H-H bonds broken.
- In this case, 4 H atoms combine to form 2 H2 molecules, so 2 H-H bonds are broken.
- Therefore, the dissociation energy of the H-H bond is equal to (-869.6 kJ / 2) = -434.8 kJ.

Conclusion:
- The dissociation energy of the H-H bond is calculated to be -434.8 kJ.
- This value represents the energy required to break one mole of H-H bonds in hydrogen gas.