# Chemical Energetics

> CIE IGCSE Chemistry · CIE IGCSE Chemistry (0620)
> Source: https://www.owlsprep.com/study/cie-0620-u5-overview/
> Weight: 8-10% of total MCQ and structured paper marks

This unit explores energy changes during chemical reactions, including classification of processes, enthalpy calculations, energy diagrams, and practical applications of reaction energetics for the CIE IGCSE 0620 syllabus.

**Prerequisites:** [CIE IGCSE Chemistry Unit 4: Chemical Bonding](https://www.owlsprep.com/study/cie-0620-u4-overview/)

## Learning objectives

- Distinguish between exothermic and endothermic reactions using experimental temperature data
- Calculate the enthalpy change of a reaction from bond energies (Extended)
- Interpret energy profile diagrams, including activation energy and catalyst effects
- Relate energetic reaction properties to real-world everyday and industrial applications

## Unit at a Glance

Chemical energetics is core to understanding how reactions release or absorb energy, and how we can harness these changes for practical use, from combustion fuels to cold packs for medical use. This unit builds a foundational understanding of energy transfer in chemistry that you will apply to later topics including reaction rates and organic chemistry.

You will start by learning to classify reactions as exothermic or endothermic, then progress to calculating enthalpy changes and interpreting energy profiles that show activation energy and the effect of catalysts on reaction energetics.

Work through the subtopic below to master all content for this unit:
- [Exothermic and Endothermic Reactions](https://www.owlsprep.com/study/cie-0620-u5-exothermic-and-endothermic-reactions/) — Learn to identify, classify, and represent exothermic and endothermic reactions using temperature data, energy level diagrams, and bond energy calculations.

## Common pitfalls

- **Wrong:** Assuming all reactions that require initial heat input are endothermic
  - Why it fails: Many exothermic reactions need heat to overcome activation energy, but release net heat to the surroundings as the reaction proceeds
  - Correct: Classify reactions based on net energy change, not just initial conditions required for the reaction to start
- **Wrong:** Mixing up the sign of enthalpy change ΔH for reaction types
  - Why it fails: ΔH is calculated as enthalpy of products minus enthalpy of reactants, so energy loss reduces the total enthalpy of the system
  - Correct: Assign ΔH < 0 for exothermic reactions and ΔH > 0 for endothermic reactions

## Cheatsheet

| Concept | Key Value/Formula | Subtopic Reference |
| --- | --- | --- |
| Exothermic Reaction | ΔH < 0, heat released to surroundings | Exothermic and Endothermic Reactions |
| Endothermic Reaction | ΔH > 0, heat absorbed from surroundings | Exothermic and Endothermic Reactions |
| Enthalpy Change | $\Delta H = H_{products} - H_{reactants}$ | Exothermic and Endothermic Reactions |
| Activation Energy | Minimum energy required for reactants to form products | Exothermic and Endothermic Reactions |
| Bond Energy Calculation (Extended) | $\Delta H = \Sigma(\text{bonds broken}) - \Sigma(\text{bonds formed})$ (energy in to break bonds, energy out when bonds form) | Exothermic and Endothermic Reactions |

## What's next

Begin your study of Chemical Energetics with the first subtopic on exothermic and endothermic reactions, where you will practice classifying reactions, drawing energy diagrams, and calculating basic enthalpy changes. After mastering this unit, you will progress to Unit 6 covering chemical reaction kinetics and rates of reaction.

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