Energy Level Diagram

  1. When a chemical reaction occurs, certain amount of heat is given off or absorb.
  2. The energy change in the chemical reaction can be presented by an energy level diagram.
  3. An energy level diagram it is a graph that shows the energy change in a chemical reaction.

Exothermic Reaction

  1. Figure below shows the general energy level diagram for exothermic reaction.
  2. We can see that the energy decreases after reaction. This is because energy is given off during an exothermic reaction.

Example

Zn + 2HCl →  ZnCl2 + H2
∆H =   126 kJ mol-1

The energy level diagram of the reaction above is as below:


Endothermic reaction

  1. Figure below shows the general energy level diagram for endothermic reaction.
  2. The energy increases after reaction. This is because energy is absorbed during an endothermic reaction.

Example
CuO + H2 → Cu + H2O
H= +130.5 kJ mol-1

The energy level diagram of the reaction above is as below:



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