Energy Level Diagrams (Oxford AQA IGCSE Combined Science Double Award)

Energy Level Diagrams

• Energy level diagrams are graphical representations of the relative energies of the reactants and products in chemical reactions

• The energy of the reactants and products are displayed on the y-axis and the reaction pathway is shown on the x-axis

• Arrows on the diagrams indicate whether the reaction is exothermic (downwards pointing) or endothermic (upwards pointing)

• The difference in height between the energy of reactants and products represents the overall energy change of a reaction

• The initial increase in energy, from the reactants to the peak of the curve, represents the activation energy required to start the reaction

• The greater the initial rise then the more energy that is required to get the reaction going e.g. more heat needed

Energy Level Diagrams

• In exothermic reactions:

  • Energy is given out to the surroundings

  • The energy of the products will therefore be lower than the energy of the reactants

  • The overall energy change is negative

  • This is represented on the reaction profile with a downwards-arrow as the energy of the products is lower than the reactants

• In endothermic reactions:

  • Energy is taken in from the surroundings

  • The energy of the products will be higher than the energy of the reactants

  • The overall energy change is positive

  • This is represented on the reaction profile with an upwards-arrow as the energy of the products is higher than the reactants