The bond dissociation energy decreases for the following bonds: H–F (570 kJ/mol), H–Cl (432 kJ/mol), H–Br (366 kJ/mol), and H–I (298 kJ/mol). Which of the statements below best explains why?

Consider the following reaction P₄(g) → 2 P₂(g) with a ΔH° value of +229.1 kJ. If the P–P bond has an average bond dissociation energy of 197 kJ/mol, estimate the value of the P≡P triple bond energy in P₂(g).

Formaldehyde, CH₂O is a pungent, colorless gas famous for its use to preserve tissues or cells. Using the bond dissociation energies and the ΔH°_f = 716.7 kJ/mol for C(g), estimate the value of ΔH°_f for CH₂O at 25.0°C. Explain why the value obtained is only an estimate. The literature value of ΔH°_f of CH₂O is –108.6 kJ/mol.

Average Bond Dissociation Energies: O=O: 498 kJ/mol, H–H: 436 kJ/mol, C–H: 410 kJ/mol, C=O: 732 kJ/mol

Acetylene in nature is formed from the thermal decomposition of long-chain hydrocarbons at high temperatures (1700 K). Acetylene is a hydrocarbon composed of two carbon and two hydrogen atoms. The decomposition reaction for acetylene is:
C₂H₂(g) → 2 C(s) + H₂(g)
Use bond energies to explain why this reaction is improbable. The bond energies are:
H-H: 432 kJ/mol
C≡C: 839 kJ/mol
C-H: 413 kJ/mol

Consider a photon with enough energy to break an N-N bond. Will the same photon be able to break an N-H bond based on average bond enthalpies?

Estimate the average molar bond enthalpy of the silicon-bromine bond in the SiBr₄ molecule using the following values:

ΔH Br(g) = 111.9 kJ/mol

ΔH Si(g) = 450.0 kJ/mol

ΔH SiBr₄(g) = –415.5 kJ/mol

Phosphoryl chloride (POCl₃) can be formed from the reaction of phosphorus trichloride (PCl₃) and oxygen gas (O₂). The unbalanced reaction is shown below:

PCl₃(g) + O₂(g) → POCl₃(g)

In POCl₃, the O atom and the three Cl atoms are bonded to the central P atom. Referring to the given in the table below, calculate the approximate enthalpy of the reaction and determine whether the reaction is endothermic or exothermic.