Bond Enthalpies

Does breaking bonds require energy, release energy, or not involve energy at all?

What kind of energy change happens in the photosynthesis reaction in plant leaves?

Is this equation endo- or exo-thermic?

PCl3 (s) + Cl2 (g) --> PCl5 (s) + energy

Is this equation endo- or exo-thermic?

2KNO3 (s) + energy --> 2KNO2 (s) + O2

How can we figure out if an overall reaction is endo- or exo-thermic? It is the difference between _______ and __________.

For the reaction 2H₂(g) + O₂(g) → 2H₂O(g) the bond enthalpies (in kJ/mol) are

H-H = x, O=O = y, O-H = z

Which calculation will give the value, in kJ/mol, of ΔH for the reaction?