Energy Level Diagram
- When a chemical reaction occurs, certain amount of heat is given off or absorb.
- The energy change in the chemical reaction can be presented by an energy level diagram.
- An energy level diagram it is a graph that shows the energy change in a chemical reaction.
Exothermic Reaction
- Figure below shows the general energy level diagram for exothermic reaction.
- 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
- Figure below shows the general energy level diagram for endothermic reaction.
- 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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