a All bond energies are endothermic because bond cleavage can only occur

A all bond energies are endothermic because bond

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a. All bond energies are endothermic because bond cleavage can only occur following the absorption of energy. b. The following table provides the bond energies for common covalent bonds in kJ/mol: Experiment #11A Barnett
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57 Table 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 state c. The enthalpy, ΔH, of a reaction is approximately equal to the sum of the bond 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 using thermochemical data is more accurate at determining the enthalpy for a reaction. Catalytic Decomposition of Hydrogen Peroxide : 1) Hydrogen peroxide, H 2 O 2 ,decomposes by disproportionation, into liquid water and 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 ), manganese dioxide (MnO 2 ), or an iron(III) catalyst (Fe 3+ ). c. The balanced equation is depicted below: H 2 O 2 ( aq ) Fe(NO 3 ) 3 H 2 O( l ) + ½ O 2 ( 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 an ANALYTICAL balance. a. These two cups should be stacked on top of one another and the cap should 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% hydrogen peroxide (H 2 O 2 ) to the calorimeter and obtain the mass on an ANALYTICAL balance. a. Ensure that no hydrogen peroxide solution is clinging to the sides of the Styrofoam cups. b. Record the mass in the data table. 3) Obtain the mass of a clean and dry 10.0 mL graduated cylinderon an ANALYTICAL balance. a. Ensure that no water is clinging to the sides of the cylinder. Experiment #11A Barnett
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58 b. Record the mass in the data table. 4) Next, measure out 10.0 mL 0.50 M Fe(NO 3 ) 3 solution into the pre-weighed graduated cylinder. a. Record the volume in the data table. 5) Measure the mass of the graduated cylinder with the added Fe(NO 3 ) 3 solution on an 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 the calorimeter to the nearest tenth to hundredth of a degree depending on the thermometer calibrations (0.1 o C – 0.01 o C). a. Record measurement in data table. 7) Transfer the Fe(NO 3 ) 3 solution into the calorimeter. a. Ensure that you do not allow any of the hydrogen peroxide solution from inside the calorimeter to splash out.
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  • Spring '19
  • Chemistry, Chemical reaction, Timothy Barnett

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