Oxygen atoms can combine with ozone to form oxygen: O3(g)+O(g) ⟶2 O2(g) ΔHrxn^∘=-394 kJ,Using

Oxygen atoms can combine with ozone to form oxygen:...

Oxygen atoms can combine with ozone to form oxygen: $$\mathrm{O}_{3}(\mathrm{g})+\mathrm{O}(\mathrm{g}) \longrightarrow 2 \mathrm{O}_{2}(\mathrm{g}) \quad \Delta H_{\mathrm{rxn}}^{\circ}=-394 \mathrm{kJ}$$,Using $\Delta H_{\mathrm{ren}}^{\circ}$ and the bond energy data in Table 9.10 estimate the bond energy for the oxygen-oxygen bond in ozone, $\mathbf{O}_{3} .$ How does your estimate compare with the energies of an $\mathrm{O}-\mathrm{O}$ single bond and an $\mathrm{O}=\mathrm{O}$ double bond? Does the oxygen-oxygen bond energy in ozone correlate with its bond order?

Key Concepts

Resonance and Delocalization

Resonance involves the mixing of different valid Lewis structures, which contributes to electron delocalization across a molecule. This results in bond energies and bond orders that are averages of the contributing structures. In molecules exhibiting resonance, such as ozone, the effective bond order and bond energy do not match those of a pure single or double bond; instead, they reflect a hybrid character that influences its reactivity and stability.

Bond Order

Bond order is a measure of the number of bonds between two atoms and is directly related to bond strength and length. A higher bond order generally leads to a stronger and shorter bond. In cases where resonance is present, the actual bond order may be fractional, indicating that the bond has character intermediate between typical single and double bonds.

Reaction Enthalpy and Hess's Law

Reaction enthalpy (?H_rxn) represents the net energy change during a chemical reaction. Hess's law states that the total enthalpy change for a reaction is the same regardless of the pathway taken. By constructing a thermochemical cycle, one can isolate the energy associated with breaking and forming specific bonds, making it possible to estimate unknown bond energies using known values and the overall reaction enthalpy.

Bond Energy Estimation

This concept involves determining the energy needed to break a specific chemical bond by comparing the reaction enthalpy with other known bond energies. It is used to predict unknown bond energies by calculating the energy difference between reactants and products in a reaction, often utilizing average bond energy values from tables or thermochemical data.

Transcript

00:01 In this question, we're asked to calculate the energy associated with breaking apart the ozone bonds to form this double oxygen.

00:13 We are given that the delta h of the reaction is negative 394 kilojoules.

00:19 The energy associated with an oxygen double bond is 498 kilojoules, and an oxygen oxygen single bond is 146 kilojoules.

00:30 Now conceptually, let's think about what we're doing.

00:33 So we have an ozone molecule.

00:41 We're adding an oxygen to make two oxygen molecules that are double bonded to each other.

00:54 So we have to break these bonds in the ozone and form these double bonds.

01:02 All right? so mathematically, what are we looking at doing? well, the delta h of the reaction, the energy associated with the whole reaction, is equal to the energy associated with, well, let's just do e for energy of breaking the bonds in the ozone, plus the energy associated with making the bonds and the oxygen.

01:42 So the energy associated with breaking the bonds plus the energy associated with making the bonds equals the net delta h of the reaction.

01:52 We know that the delta h of the reaction is minus 394 kilojoules.

01:59 I'm going to leave out units in the writing of this question.

02:07 We're trying to find the energy associated with the breaking of the ozone bonds.

02:13 And there's two bonds we're going to break.

02:16 So let's just say 2x.

02:21 Because of the resonance structures, remember we have ozone like this versus ozone like this, we really have something in between these two resonant structures.

02:38 So the bond order associated with each of those ozone bonds is about 1 .5.

02:44 And they're theoretically equivalent.

02:47 So suffice to say, we use 2x in our equation.

02:53 And then we have to add the energy associated with making these 2 -02 bonds.

03:01 Now, the sign is important, right? we know that forming bonds is an energetically favorable process.

03:12 You release energy when you form bonds.

03:16 So that means it's a negative value...