Question

Which of the following options correctly describe the procedure used to calculate ΔH for a reaction using bond energies? Select all that apply.

A. ΔHbonds formed is always endothermic.
B. ΔH for the reaction is given by
(sum of ΔHbonds broken) + (sum of C. ΔHbonds formed)
D. ΔH is obtained by adding together the absolute values of the bond energies for all bonds broken and formed.
E. The sum ΔHbonds broken is given a positive value.

Answer 1

To calculate ΔH for a reaction using bond energies, sum the energy required to break all bonds in the reactants and subtract the energy released when all bonds are formed in the products.

Step-by-step explanation:

The procedure used to calculate ΔH for a reaction using bond energies is to sum the energy required to break all bonds in the reactants (energy "in", positive sign) and subtract the energy released when all bonds are formed in the products (energy "out," negative sign). The enthalpy change is given by the equation: ΔH = Σ(ΔHbonds broken) - Σ(ΔHbonds formed)

Option A is incorrect because ΔHbonds formed can be either endothermic or exothermic, depending on whether the bonds in the products are stronger or weaker than the bonds in the reactants.

Option D is incorrect because ΔH is not obtained by adding together the absolute values of the bond energies for all bonds broken and formed, but by subtracting the bond energies of formed bonds from the bond energies of broken bonds.