Energy Diagrams

1. Energy Diagrams Depicting energy transfers

2. Energy Diagrams defined • Energy diagrams show how a reaction works. • Energy diagrams display • The energy of reactants and products • The energy needed for a reaction to occur • The energy absorbed or released due to reaction

3. Here’s a Potential Energy Diagram! The curve represents the energy levels of the reactants, the reaction and finally the products. The reaction coordinate shows the direction of the reaction, the start is on the left, the end is on the right side of the graph.

4. A The REACTANTS get together at the start of the reaction and have a certain potential energy, which in this graph is “A”. The measure of this energy is usually in kilojoules (kJ).

5. D The PRODUCTS have a potential energy when they are finally produced, which is “D”. The products are formed at THE END OF THE REACTION, on the right hand part of this curve.

6. * B At the peak of the energy curve is the ACTIVATED COMPLEX. This is when the reactants are in the process of being converted into products. The amount of energy it takes to start this reaction is “B”. This is called the ACTIVATION ENERGY. Activation energy can be calculated in the following manner: ENERGYACTIVATED COMPLEX - ENERGYREACTANTS

7. C The change in enthalpy, H, is represented by “C.” This can be calculated in the following manner: ENERGYPRODUCTS - ENERGYREACTANTS

8. Putting Pieces Together Activated Complex Activation Energy of forward reaction, Ea Ea = AC - Reactants Reactants Enthalpy of forward reaction, DH Products DH = Products - Reactants Energy Reaction

9. Types of Energy Diagrams • Endothermic – the reaction absorbs heat so DH is positive • The reactants have less potential energy than the products A - - - B AB DH > 0 A + B

10. Types of Energy Diagrams • Exothermic – the reaction releases heat so DH is negative • The reactants have more potential energy than the products A - - - B A + B DH < 0 AB