Energy level diagrams, activation energy, the sign of ΔH and what a catalyst changes.
What you will learn
- Read the activation energy and ΔH from a profile
- Say whether a profile is exothermic or endothermic
- Explain what a catalyst does to the profile
Up the hill, then down
A reaction profile shows the energy of the reactants, the products, and the hump in between.
- Activation energy: the minimum energy colliding particles need to react. It is the height of the hump above the reactants.
- ΔH (overall energy change) = energy of products − energy of reactants. Negative for exothermic (products lower), positive for endothermic.
- reactants 200 kJ/mol, peak 320 kJ/mol, products 120 kJ/mol
- activation energy = 320 − 200 = 120 kJ/mol
- ΔH = 120 − 200 = −80 kJ/mol: exothermic
The rest of this lesson and its 10 practice questions are locked.
In this lesson
- Up the hill, then down
- Catalysts lower the hump
10 practice questions, marked as you go; about 20 minutes in all.
Key terms
Reactants, Lower activation energy
In this unit: Energy changes
Exothermic and endothermic reactions, the temperature change practical, reaction profiles, bond energies, cells and fuel cells.