 Okay, so let's try this one. It says, for the reaction that's pictured, oxygen plus molecular oxygen goes to ozone. The standard enthalpy of that reaction is negative 107.2 kJ per mole. Calculate the average bond enthalpy in ozone or O3. Okay, so in order to do this, you have to remember how to get your overall enthalpy from your bond energies. Okay, so if you recall, the delta H of the reaction is going to equal the sum of the bond energies of the reactants minus the sum of the bond energy of the products like that. Okay, so what we want is the bond energy of the products overall. Okay, and then we're going to actually divide that by two because there's two bonds in this thing. Okay, we'll look at that in a second. So how do we do this? Let's rearrange this equation to solve for that sum of bond energy. Okay, so we'll take this to the other side, so we'll get a negative sum of the bond energy of the products equals delta H of the reaction minus the sum of the bond energies of the reactants like that. Okay, so we want this to be positive, so we're going to multiply everything by negative one. Okay, so when we do that, we're going to get the sum of the bond energy of the products equals the sum of the bond energy of the reactants plus, I'm sorry, minus minus the delta H of the reaction. So you set with that? So I'm going to erase this portion up here and then we'll just redo this equation and we'll plug and choke. Okay, so in other words the sum of the bond energies of O3 equals the sum of the bond energies of the reactants, but this reactant doesn't have any bonds in it. Okay, so this is the only reactant that has bonds, so we'll do that minus the delta H of the reaction, which we've got up there. Okay, so this is in kilojoules per mole, that's in kilojoules per mole, so we just plug and choke, so we got 498.7 kilojoules per mole minus a minus 107.2 kilojoules per mole, like that. So 498.7 plus 107.2, which gives us a total energy of 605.9 kilojoules per mole. So that's the total bond energy of O3, but we're looking for the average bond energy of O3. Remember O3's structure, so there's going to be one, two bonds there. Okay, so how do we figure out what the average bond energy is? Well, there's two of them, right? So the energy is going to be, well, the total bond energy divided by the number of bonds, right? So bond energy total divided by the number of bonds. So that's going to be 605.9 kilojoules per mole divided by 2. So when we do that, we just take that number, divide it by 2, and get 303.0 kilojoules per mole for the average bond energy of O3. Any questions on that one? No, it's okay. Okay, good. That's a good question. I don't think we have any recordings of that.