---
title: "Reaction Profiles and Activation Energy"
description: "Draw a reaction as energy against progress, marking reactants, products, the overall energy change and the activation energy hump that has to be climbed before anything happens."
canonical: https://lightmysky.com/learn/science/reaction-profiles-and-activation-energy-mt_6LtFkXn_xQ
source: https://lightmysky.com/learn/science/reaction-profiles-and-activation-energy-mt_6LtFkXn_xQ.md
retrieved: 2026-09-12
---

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# Reaction Profiles and Activation Energy

Draw a reaction as energy against progress, marking reactants, products, the overall energy change and the activation energy hump that has to be climbed before anything happens.

Subject: Science · Area: Matter & Materials · Ages 15 to 16
Page: https://lightmysky.com/learn/science/reaction-profiles-and-activation-energy-mt_6LtFkXn_xQ

## Ready when they can

- Draws and labels the profile for an exothermic and for an endothermic reaction
- Reads the overall energy change and the activation energy off a given profile
- Explains why an exothermic reaction still needs energy put in to start
- Matches a temperature rise or fall measured in a beaker to the correct profile shape

## Lesson: Reading the hill a reaction climbs

A reaction profile plots energy against progress. The reactants start at one level and the products settle at another. Between them rises a hump, and the climb from reactants to the top is the activation energy. That hump is the entry fee every reacting pair must pay.

In an exothermic reaction the products sit below the reactants, and the drop leaves as heat. Burning methane looks like this. In an endothermic reaction the products sit above the reactants, and the rise is heat taken in. The shape alone tells you which kind you face.

**Example.** Read numbers off a labelled profile. Take reactants at 0, the peak at 120 and products at -80. The activation energy is peak minus reactants: 120 minus 0 is 120. The overall change is products minus reactants: -80 minus 0 is -80. A negative overall value marks an exothermic reaction.

**Tip.** Even an exothermic reaction needs a start. The spark on methane lifts a few molecules over the hump, and the heat they release lifts the rest. In the lab, a beaker that warms up matches the drop shape, and one that cools down matches the rise.

**Recap.** Profiles show the hump to climb and the drop or rise that decides heat out or in.

## Practice

8 questions on this page, each with its working shown.

## Needs first

- [Reactions That Release or Absorb Heat](https://lightmysky.com/learn/science/reactions-that-release-or-absorb-heat-mt_UoqUPI_uNz)

## Opens up

- [Enthalpy Change, Standard Conditions and Calorimetry](https://lightmysky.com/learn/science/enthalpy-change-standard-conditions-and-calorimetry-mt_GPgwgyqyvN)
- [Rates of Reaction: Collision Theory and What Changes a Rate](https://lightmysky.com/learn/science/rates-of-reaction-collision-theory-and-what-changes-a-rate-mt_Ma2bOotr9g)
- [The Arrhenius Equation and Finding Activation Energy](https://lightmysky.com/learn/science/the-arrhenius-equation-and-finding-activation-energy-mt_QBQDSNwbXK)
- [Bond Energies and the Overall Energy Change](https://lightmysky.com/learn/science/bond-energies-and-the-overall-energy-change-mt_VI0_1ogIOy)