See the calculation on this YouTube video

Solution It is best to sketch the molecules and their bonds in order to make sure that none are missed.

Thus      ?H° = ?D (bond broken) – ?D (bond formed)

                   = 4 D_C?H + 2D_O=O – 2D_C=O – 4D_O?H

                   = (4 × 416 + 2 × 498 – 2 × 803 – 4 × 467) kJ mol^–1

                   = – 814 kJ mol^–1