Energy profile diagrams show how the energy of a reaction changes from reactants to products. They help us understand whether a reaction is exothermic or endothermic and how much energy is needed to start it.

What do energy profile diagrams show?

• The relative energy of the reactants and products
• The activation energy needed to start the reaction
• Whether energy is released or absorbed overall

Exothermic reactions

• Energy is released to the surroundings
• Products have less energy than reactants
• The temperature increases
• Energy goes down on the diagram

Reactants start high, curve rises slightly (activation energy), then drops to lower products
🔽 Energy change shown as an arrow from reactants to products

Endothermic reactions

• Energy is taken in from the surroundings
• Products have more energy than reactants
• The temperature decreases
• Energy goes up on the diagram

Reactants start low, curve rises to products higher than reactants
🔼 Energy change shown as an arrow going upwards

Activation energy (Ea)

• The minimum energy needed to start a reaction
• Shown as the peak on the energy profile diagram
• All reactions need activation energy to break bonds in reactants

💡 The higher the activation energy, the more difficult it is to start the reaction.

Comparing diagrams