Answer:
D +405.0kJ mol-¹
Explanation:
Since bond energy is the energy required to break a bond, the energy of dissociation of X₂H₆ = +2775 kJmol⁻¹.
Since there is one X-X bond and six X-H bonds,
Bond energy of one X-X bond + Bond energy of six X-H bonds = energy of dissociation of X₂H₆.
Since bond energy of one X-H bond = 395 kJ mol⁻¹, then
Bond energy of one X-X bond + Bond energy of six X-H bonds = energy of dissociation of X₂H₆
Bond energy of one X-X bond + 6 × one X-H bond = +2775 kJmol⁻¹.
Bond energy of one X-X bond + 6 × 395 kJ mol⁻¹ = +2775 kJmol⁻¹.
Bond energy of one X-X bond + 2370 kJ mol⁻¹ = 2775 kJmol⁻¹
Bond energy of one X-X bond = 2775 kJmol⁻¹ - 2370 kJ mol⁻¹
Bond energy of one X-X bond = +405 kJmol⁻¹
