a.All bond energies are endothermic because bond cleavage can only occurfollowing the absorption of energy.b.The following table provides the bond energies for common covalentbonds in kJ/mol:Experiment #11A Barnett
57Table A: Bond Energies for Common Covalent Bonds in kJ/mol* Bond Bond Energy Bond Bond Energy C – H 411 O – H 459 C – O 358 O – O 142 C = O 745 O = O 494 C – C 346 C – N 305 C = C 602 C ≡ N 887 C ≡ C 835 N – H 386 *Assuming gaseous statec.The enthalpy, ΔH, of a reaction is approximately equal to the sum of thebond energies (BE) of the reactants minus the sum of the bond energies(BE) of the products.i.ΔH = Σ nBE(bonds broken)– Σ nBE(bonds formed)ii.Note: This method is only an approximation and usingthermochemical data is more accurate at determining the enthalpyfor a reaction.Catalytic Decomposition of Hydrogen Peroxide: 1)Hydrogen peroxide, H2O2,decomposes by disproportionation, into liquid waterand oxygen gas.a.This decomposition is spontaneous at room temperature but quite slow.b.It can be catalyzed by the addition of the iodide ion (I–), manganesedioxide (MnO2), or an iron(III) catalyst (Fe3+).c.The balanced equation is depicted below:H2O2(aq) Fe(NO3)3H2O(l) + ½ O2(g) Procedure for the Heat of Reaction via Calorimetry: 1)Obtain the mass of two clean and dried empty Styrofoam cups with a cap on anANALYTICAL balance.a.These two cups should be stacked on top of one another and the capshould have a hole in it to facilitate the use of your thermometer.b.This set of Styrofoam cups will function as your calorimeter.c.Record mass in data table.2)Using a clean and dry graduated cylinder, add 50.0 mL of 3.0% hydrogenperoxide (H2O2) to the calorimeter and obtain the mass on an ANALYTICALbalance.a.Ensure that no hydrogen peroxide solution is clinging to the sides of theStyrofoam cups.b.Record the mass in the data table.3)Obtain the mass of a clean and dry 10.0 mL graduated cylinderon anANALYTICAL balance.a.Ensure that no water is clinging to the sides of the cylinder.Experiment #11A Barnett
58b.Record the mass in the data table.4)Next, measure out 10.0 mL 0.50 MFe(NO3)3solution into the pre-weighedgraduated cylinder.a.Record the volume in the data table.5)Measure the mass of the graduated cylinder with the added Fe(NO3)3solution onan ANALYTICAL balance.a.Ensure that no water or solution is clinging to the sides of the cylinder.b.Record the mass in the data table.6)Measure the stable temperature of the hydrogen peroxide solutionin thecalorimeter to the nearest tenth to hundredth of a degree depending on thethermometer calibrations (0.1oC – 0.01oC).a.Record measurement in data table.7)Transfer the Fe(NO3)3solution into the calorimeter.a.Ensure that you do not allow any of the hydrogen peroxide solution frominside the calorimeter to splash out.
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