Energy Level Diagrams (Edexcel IGCSE Chemistry)

• 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 progress of the reaction 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 enthalpy change of a reaction

Energy level diagrams

Energy level diagram of an exothermic reaction and an endothermic reaction

• Energy is given out in exothermic reactions
  • The energy of the products will be lower than the energy of the reactants, so the change in energy is negative
  • This is represented on the energy level diagram with a downwards arrow as the energy of the products is lower than the reactants
• Energy is taken in in endothermic reactions
  • The energy of the products will be higher than the energy of the reactants, so the change in energy is positive
  • This is represented on the energy level diagram with an upwards arrow as the energy of the products is higher than the reactants