Chap 5 Chemical Energetics

• Exothermic reaction


  Transfers thermal or heat energy to the surroundings, leading to an increase in the temperature of the surroundings
• Endothermic reaction


  Takes in thermal or heat energy from the surroundings, leading to a decrease in the temperature of the surroundings
• Reaction pathway diagram


  Also known as an energy level diagram, shows the energies of both the reactants and final products in chemical reactions
• Exothermic reaction


  Total chemical energy of the reactants is more than that of the products, resulting in the transfer of this energy difference to the surroundings in the form of heat
• Endothermic reaction


  Chemical energy of the reactants is less than that of the products, causing the transfer of this energy difference from the surroundings to the chemicals involved
• Activation energy


  The minimum energy that colliding particles must have in order to react
• Enthalpy change


  The transfer of thermal energy during a reaction, symbol Delta H
• Enthalpy change is negative for exothermic reactions and positive for endothermic reactions
• Calculating enthalpy change using bond energies

  1. Write the balanced equation for the reaction

  2. Find the energy in (total bond energies for all the bonds in the reactants)

  3. Find the energy out (total bond energies for all the bonds in the products)

  4. Calculate the enthalpy change (energy taken in - energy given out)
• Bond making is an exothermic process and bond breaking is an endothermic process
• Whether a reaction absorbs or releases energy depends on how much energy it takes to break old bonds compared to how much is released when new bonds form