bond energy calculations

• What should you be able to do by the end of the two-part video on bond energies?

  Use bond energies to calculate the energy change for a chemical reaction
• What happens to energy in exothermic reactions?

  Energy is transferred from the chemicals to the surroundings
• How are energy changes represented in exothermic reactions?

  Energy changes are shown as negative
• What occurs in endothermic reactions regarding energy transfer?

  The chemicals gain energy from the surroundings
• How are energy changes represented in endothermic reactions?

  Energy changes are shown as positive
• What is the relationship between breaking and making chemical bonds in terms of energy?

  Breaking bonds requires energy and is endothermic, while making bonds releases energy and is exothermic
• What is the energy value for breaking the bond between hydrogen atoms?

  436 KJ per mole
• What is the energy value for breaking the bond between chlorine atoms?

  242 KJ per mole
• How do you calculate the total energy needed to break all chemical bonds in the reaction?

  Add the energy values for breaking the bonds
• What is the energy released when making the bond between hydrogen and chlorine atoms?

  431 KJ per mole
• How many molecules of hydrogen chloride are produced in the reaction?

  Two molecules
• How do you calculate the total energy released when making the bonds in the reaction?

  Multiply the energy value by two
• What does a negative sign in front of the energy value indicate in the context of bond making?

  Energy leaves the reaction
• How do you calculate the final energy change for the reaction?

  Subtract the total energy released from the total energy required
• What is the final energy change for the reaction between hydrogen and chlorine?

  • 184 KJ
• What does a final energy change of -184 KJ indicate about the reaction?

  The reaction is exothermic
• What are the steps to calculate the energy change for a chemical reaction using bond energies?

  1. Identify the bonds broken and made in the reaction.
  2. Find the energy values for each bond.
  3. Calculate the total energy required to break the bonds (positive values).
  4. Calculate the total energy released when making the bonds (negative values).
  5. Subtract the total energy released from the total energy required to find the final energy change.
• What are the key differences between exothermic and endothermic reactions?

  • Exothermic reactions:
  • Energy is transferred to surroundings
  • Energy changes are negative
  • Endothermic reactions:
  • Chemicals gain energy from surroundings
  • Energy changes are positive
• What should you be able to do by the end of the two-part video on bond energies?

  Use bond energies to calculate the energy change for a chemical reaction
• In the reaction of hydrogen and oxygen to form water, how many molecules of hydrogen are reacting?

  Two molecules of hydrogen
• What is the bond energy needed to break the bond between two hydrogen atoms?

  436 KJ per mole
• What does the positive sign in bond energy indicate when breaking bonds?

  It shows that energy is being put in to break the bonds
• How much total energy is needed to break the bonds in the reaction of hydrogen and oxygen?

  1,367 KJ
• What is the bond energy for an oxygen to hydrogen bond?

  463 KJ per mole
• How do you calculate the overall energy change for the reaction of hydrogen and oxygen?

  Subtract the total energy released from the total energy input
• What does a negative total energy change indicate about a reaction?

  It shows that the reaction is exothermic
• In the combustion of methane, how many carbon to hydrogen bonds are present in one molecule of methane?

  Four carbon to hydrogen bonds
• What is the bond energy of a carbon to hydrogen bond?

  413 KJ per mole
• How do you calculate the total bond energy needed to break all bonds in methane and oxygen?

  Add the bond energies of all broken bonds
• What is the total bond energy needed to break the bonds in the combustion of methane?

  2,642 KJ
• What is the bond energy of the carbon to oxygen bond in carbon dioxide?

  799 KJ per mole
• How do you calculate the total energy change for the combustion of methane?

  Subtract the total energy released from the total energy input
• What is the final energy change value for the combustion of methane?

  • 88 KJ
• What are the steps to calculate energy change using bond energies?

  1. Identify bonds broken and their energies (positive values).
  2. Identify bonds formed and their energies (negative values).
  3. Calculate total energy input and output.
  4. Subtract total energy output from total energy input.
• What is the significance of bond energies in chemical reactions?

  • Helps predict energy changes during reactions
  • Determines whether a reaction is exothermic or endothermic
  • Essential for calculating reaction enthalpy