an alternate route for the reaction. used up during the reaction. Copy and complete: An ______________________ can be used to show how the energy stored in chemicals changes during a chemical reaction. In ______________ reactions the products have more energy than the ___________. In exothermic reactions the ____________ have less energy than the __________. A catalyst __________ the __________ energy. It does this by providing __________________________ ________. A catalyst is not ________________________. energy level diagram endothermic reactants products reactants lowers activation an alternate route for the reaction. used up during the reaction.

Bond Energies Objective: to explain how the balance of energy changes when bonds are broken or made, and how this affects the overall energy change of a reaction. Outcomes: Most: I can assign bond energies to an energy level diagram (6) Some: I can calculate the energy transferred in reactions using supplied bond energies (9/8) Keywords: energy level diagram, exothermic, endothermic, bond energy Homework: Due: Thursday 21 March 2 2 2 2

Watch https://www.youtube.com/watch?v=5- TPVHIi39w

Review the energy level diagram below: Which energy change, A, B or C, represents the activation energy? B Which energy change, A, B or C, shows that the reaction is exothermic? A B Why does a mixture of hydrogen and oxygen need a spark or flame to start the reaction? A

bond breaking = energy IN ENDOTHERMIC bond making = energy OUT I can state what happens to energy when bonds are made and broken (5) bond breaking = energy IN ENDOTHERMIC bond making = energy OUT EXOTHERMIC

has a bond energy of 436kJ/mol Each bond has a different bond energy. The amount of energy it takes to make OR break it. A H-H bond has a bond energy of 436kJ/mol Data on bond energies can be used to calculate the TOTAL energy of a reaction. This is the difference between the energy put in when bonds are made and the energy given out when bonds are broken.

CH4(g) + 2O2(g) CO2(g) +2H2O(l) Example to review with class if necessary or just go round and help individuals before going through. Draw out the molecules to support showing the bonds, particularly the double bond for oxygen. Work out the bond energies for: a) the reactant molecules b) the product molecules Hence c) workout the total energy for the reaction. I can calculate the energy transferred in reactions using supplied bond energies (9/8)

CH4(g) + 2O2(g) CO2(g) +2H2O(l) CH4(g) + 2O2(g) CO2(g) +2H2O(l) ____________ ________ ______ ______ Add labels and energy values to the energy level diagram for the reaction. Ask them what an energy level diagram would look like for an endothermic reaction I can assign bond energies to an energy level diagram (6/7)

Complete 5 examples to be done around the room specific examples on big paper... Use the 5 print out examples at the end of the ppt.

Bond Energies Objective: to explain how the balance of energy changes when bonds are broken or made, and how this affects the overall energy change of a reaction Outcomes: I can state what happens to energy when bonds are made and broken (5) I can assign bond energies to an energy level diagram (6) I can calculate the energy transferred in reactions using supplied bond energies (8/9) Keywords: energy level diagram, exothermic, endothermic, bond energy Homework: Due: Thursday 21 March 13 13 13 13

Example 1 Ethanol + Oxygen Water + Carbon Dioxide C-H 413 O=O 498 a) Complete the balanced symbol equation. b) Draw the structural formula. c) Calculate the energy in for the reactant bonds being broken. d) Calculate the energy out for the product bonds being made. e) Work out the overall change in energy BOND ENERGY (kJ/mol) C-H 413 O=O 498 C-C 347 C=O 732 O-H 464 5 Examples to be printed out and given to small groupspairs of students to work out. Swapping after 5-10 minutes depending on how they get on with them. Peer marking can also be done if appropriate

Example 2 Propane + Oxygen Water + Carbon Dioxide C-H 413 O=O 498 a) Complete the balanced symbol equation. b) Draw the structural formula. c) Calculate the energy in for the reactant bonds being broken. d) Calculate the energy out for the product bonds being made. e) Work out the overall change in energy BOND ENERGY (kJ/mol) C-H 413 O=O 498 C-C 347 C=O 732 O-H 464

Example 3 Hydrogen + Nitrogen Ammonia H-H 436 N-H 391 N≡N 945 a) Complete the balanced symbol equation. b) Draw the structural formula. c) Calculate the energy in for the reactant bonds being broken. d) Calculate the energy out for the product bonds being made. e) Work out the overall change in energy BOND ENERGY (kJ/mol) H-H 436 N-H 391 N≡N 945

Example 4 Hydrogen + Oxygen Water O=O 498 H-H 436 O-H 464 a) Complete the balanced symbol equation. b) Draw the structural formula. c) Calculate the energy in for the reactant bonds being broken. d) Calculate the energy out for the product bonds being made. e) Work out the overall change in energy BOND ENERGY (kJ/mol) O=O 498 H-H 436 O-H 464

Example 5 – A/S level question CHM2 Jan 2009