Activation Energy

Part of the Energy, Rates and Equilibrium section of Coddy's Chemistry journey. Lesson 4 of 35.

The activation energy E_a is the least energy colliding particles need to react: the hump's height above the reactants.

Exothermic: the products are lower than the reactants

An exothermic reaction can still need a spark: a match lifts the first particles over the hump.

The reverse reaction climbs from the products: its activation energy is $E_a - \Delta H$ .

Challenge

The reaction that makes ammonia gives out $90\ \mathrm{kJ}$ and has an activation energy of $230\ \mathrm{kJ}$ without a catalyst (rounded to the diagram's scale). Draw its energy diagram.

Try it yourself

Energy diagramDraw the energy diagram

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

All lessons in Energy, Rates and Equilibrium

1Energy in Reactions

Exothermic and Endothermic Energy Diagrams Enthalpy ChangeActivation EnergyRecap - Hand Warmer

4Rates of Reaction

Collision Theory Concentration and Rate Temperature and Rate Surface Area Catalysts Recap - Speed Trials

7Practice Problems

Recap - Methanol Plant Recap - Butane Lighter Recap - Limestone Kiln

2Bond Energies

Breaking and Making Bonds Delta H from Bond Energies Hess's Law Energy and Moles Recap - Fuel Value

5Equilibrium

Reversible Reactions Dynamic Equilibrium The Equilibrium Constant Writing K Solids and Liquids in K Recap - K Builder

3Changes of State

Heating Curves Melting and Boiling Energy of State Changes Recap - Ice to Steam

6Changing an Equilibrium

Le Chatelier's Principle Changing Concentration Changing Pressure Changing Temperature The Haber Process Recap - Factory Settings