Chapter 9.4: Bond Energy and Chemical Change

Flashcards from Chapter 9.4 of Chemistry: The Molecular Nature of Matter and Change.

Enthalpy of reaction (ΔH°_rxn)

This arises from the differences between reactant and product bond energies

• Defined as ΣΔH°_{bonds broken} + ΣΔH°_{bonds formed}

  • Also defined as ΣBE_{bonds broken} - ΣBE_{bonds formed}

• Results from absorption during breakage, and emittance during formation, using Hess’s Law

Hess’s Law

States that the enthalpy of a reaction is equal to the sum of the enthalpies taken to get to an end point regardless of method

• Enables the calculation of ΔH°_rxn through the breakage and formation of all bonds to obtain an average

Fuel

Any material that reacts with O₂ to release energy, featuring weak bonds

• Less energy is absorbed in breakage than released in formation

• Energy yield depends on number of O bonds present

Strong bonds

The presence of these results in a stronger material as more energy is needed to break them

• Seen in forever chemicals, preventing their breakdown in nature