1) Identify the axes.
The Y-axis refers to the energy in the reactants and in the products,
The X-axis refers to the progress of the reaction.
2) Important points in the diagram.
A: Potential energy in the reactants.
B: Activation energy. The energy that must be provided so the reaction occurs.
C: Potential energy in the products.
3) Enthalpy change calculation.
We calculate the enthalpy change using the following calculation:
[tex]\Delta H=\Sigma n\Delta H_{(reactants)}-\Sigma n\Delta H_{(products)}[/tex]
4) Analysis.
If the potential energy is higher in the reactants, the enthalpy change is positive. This means the reaction is exothermic.
If the potential energy is higher in the products, the energy change is negative. This means the reaction is endothermic.
5) Diagram
The red circle marks the potential energy in the reactants and it is higher than the potential energy in the products (blue circle).
This diagram represents a positive enthalpy change.
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