Edexcel IGCSE Chemistry 复习笔记 3.1.4 Energy Level Diagrams

Energy Level Diagrams

• Energy level diagrams (sometimes called reaction profiles) 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 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

Reaction profile 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 reaction profile with a downwards-arrow as the energy of the products is lower than the reactants
• Energy is taken 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 reaction profile with an upwards-arrow as the energy of the products is higher than the reactants