Homeschool Guide: These lesson plans are a guide for parents. Content may contain errors — always cross-reference with official exam board specifications.

exothermic and endothermic reactions

FoundationHigherAll Boards

4 detailed 50-minute lessons with teaching scripts, worked examples, parent guides, and assessment criteria.

Fastmail

Lesson Overview

Total Lessons: 4
Tier: Foundation and Higher
Duration: 50 minutes per lesson (200 minutes total)
Exam Boards: AQA, Edexcel, OCR, Eduqas, CCEA

Learning Objectives

Prerequisites

Materials & Equipment

Lesson 1: Introduction: exothermic and endothermic reactions

Duration: 50 minutes

Starter Activity (5 minutes)

Quick Recall

Write down everything you already know about exothermic and endothermic reactions. Then check against the key terms: Exothermic reaction, Endothermic reaction, Activation energy. Use a mini-whiteboard or paper.

Main Content (35 minutes)

Parent/Teacher Guide:
Before lesson: Read the script below. Pre-teach key vocab: Exothermic reaction, Endothermic reaction, Activation energy.
If stuck: Re-read the revision notes (link above), then break the content into smaller steps.
Extension: See the Stretch & Challenge ideas in Lesson 4.
Teaching Script (35 mins):
Mins 0-5 - Hook: "Today: exothermic and endothermic reactions. By the end you will be able to answer exam questions on it unaided. It connects to the rest of Chemistry because the ideas here recur across the spec."
Mins 5-20 - Direct Instruction: Work through the core ideas below one at a time; after each, ask your student to explain it back in their own words.
Mins 20-30 - Guided Practice: Model the worked example together, then let your student attempt the first practice question with guidance.
Mins 30-35 - Independent Practice: 2-3 practice questions from Lesson 3 below, with immediate feedback.
First Look

Start with the revision notes summary, then attempt: Foundation Define exothermic and endothermic reactions.

Plenary (5 minutes)

Check Out

Your student states one thing they learned and one question they still have about exothermic and endothermic reactions.

Lesson 2: Core Concepts: exothermic and endothermic reactions

Duration: 50 minutes

Starter Activity (5 minutes)

Review Previous Lesson

Quick recap: write 3 key points from Lesson 1 on exothermic and endothermic reactions. Check them against the notes below.

Main Content (35 minutes)

Exothermic reaction: A reaction that releases energy to the surroundings, causing the temperature of the surroundings to increase. Energy is transferred from the reactants to the surroundings.
Endothermic reaction: A reaction that absorbs energy from the surroundings, causing the temperature of the surroundings to decrease. Energy is transferred from the surroundings to the reactants.
Activation energy: The minimum amount of energy that particles must have to react when they collide. Shown on reaction profiles as the energy "hill" from reactants to the peak.
Bond energy: The amount of energy needed to break a particular chemical bond, or the amount released when the bond forms. Breaking bonds is endothermic; making bonds is exothermic.
Reading reaction profiles: Exothermic: Products are at a lower energy level than reactants. The arrow showing energy change points downwards. Endothermic: Products are at a higher energy level than reactants. The arrow showing energy change points upwards. Activation energy: The arrow from reactants up to the peak of the curve. Both exothermic and endothermic reactions have activation energy.

Practice (10 minutes)

Q: Foundation Define exothermic and endothermic reactions.

Answer: Exothermic: releases energy to surroundings, temperature increases. Endothermic: absorbs energy from surroundings, temperature decreases.

Plenary (5 minutes)

Explain Back

Your student teaches the key points back to you without looking. Fill any gaps immediately.

Lesson 3: Application: exothermic and endothermic reactions

Duration: 50 minutes

Starter Activity (5 minutes)

Quick Recall

Recall the key terms: Exothermic reaction, Endothermic reaction, Activation energy. Define each in one sentence.

Main Content (35 minutes)

Parent/Teacher Guide: Let your student attempt each question alone first, then compare with the model answer. Award method marks for correct working even if the final answer is wrong.

Q1: Foundation Define exothermic and endothermic reactions.

Answer: Exothermic: releases energy to surroundings, temperature increases. Endothermic: absorbs energy from surroundings, temperature decreases.

Q2: Foundation Classify each of the following as exothermic or endothermic: combustion, thermal decomposition, neutralisation, photosynthesis.

Answer: Combustion = exothermic. Thermal decomposition = endothermic. Neutralisation = exothermic. Photosynthesis = endothermic.

Q3: Higher For the reaction N₂ + 3H₂ → 2NH₃, calculate the energy change. Bond energies: N≡N = 945, H−H = 436, N−H = 391 (all kJ/mol).

Answer: Energy in (breaking): N≡N + 3(H−H) = 945 + (3 × 436) = 945 + 1308 = 2253 kJ/mol. Energy out (making): 6 × N−H (because 2NH₃ has 6 N−H bonds) = 6 × 391 = 2346 kJ/mol. Energy change = 2253 − 2346 = −93 kJ/mol (exothermic).

Q4: Foundation Describe how the reaction profile of an exothermic reaction differs from that of an endothermic reaction.

Answer: Exothermic: products at lower energy level than reactants, energy change arrow points down. Endothermic: products at higher energy level, energy change arrow points up. Both have activation energy (the hill from reactants to the peak).

Q5: Higher Explain, in terms of bond breaking and bond making, why combustion reactions are exothermic.

Answer: In combustion, the bonds formed in the products (C=O and O−H) release more energy than was needed to break the bonds in the reactants (C−H and O=O). Since more energy is released making bonds than absorbed breaking bonds, the reaction is exothermic.

Plenary (5 minutes)

Error Review

Review any questions answered incorrectly. Identify whether the error was knowledge, method, or reading the question.

Lesson 4: Exam Practice: exothermic and endothermic reactions

Duration: 50 minutes

Starter Activity (5 minutes)

Command Words

Review what these command words require: state (one point), describe (say what happens), explain (say why), compare (both sides), evaluate (judgement).

Main Content (35 minutes)

Extended Answer

Extended question: Extended Answer 6 marks: Explain exothermic and endothermic reactions using bond energies. <div class="

In a chemical reaction, bonds in the reactants must first be broken, which requires energy (endothermic). New bonds then form in the products, which releases energy (exothermic). If the energy released when new bonds form is greater than the energy needed to break the original bonds, the reaction is exothermic — more energy is given out than taken in, so the surroundings get warmer and ΔH is negative. If the energy needed to break bonds is greater than the energy released making new bonds, the reaction is endothermic — more energy is taken in than given out, the surroundings get cooler and ΔH is positive. For example, combustion is exothermic because the C=O and O−H bonds formed in CO₂ and H₂O release more energy than was needed to break the C−H and O=O bonds in the reactants. Mark scheme: 1 mark for bond breaking requires energy; 1 mark for bond making releases energy; 1 mark for exothermic = more energy released than absorbed; 1 mark for endothermic = more energy absorbed than released; 1 mark for correct sign of ΔH; 1 mark for combustion example.

Exam Tips: In bond energy calculations, always count the number of each type of bond carefully — check the formulae | A negative energy change means exothermic; a positive value means endothermic | Breaking bonds is always endothermic (energy in); making bonds is always exothermic (energy out) | On reaction profiles, the activation energy arrow always goes upwards from the reactants line | Remember that both exothermic AND endothermic reactions need activation energy to get started | When asked to sketch a reaction profile, label the axes (energy on y-axis, reaction progress on x-axis), the activation energy, and the overall energy change
Common Errors: Watch Out! Breaking bonds releases energy. Wrong: breaking bonds releases energy Correct: breaking bonds requires energy (endothermic); making bonds releases energy (exothermic) Exothermic reactions are always fast. Wrong: exothermic reactions are always fast Correct: the speed of a reaction (rate) is independent of the energy change — an exothermic reaction can be slow (e.g. rusting) and an endothermic reaction can be fast
AO3 - Reasoning & Interpretation: Analysis and Evaluation A student investigates the reaction between hydrogen and chlorine: H₂ + Cl₂ → 2HCl. Bond energies: H−H = 436, Cl−Cl = 242, H−Cl = 431 kJ/mol. Question: Calculate the enthalpy change. Is the reaction exothermic or endothermic? A student says "the H−Cl bond is weaker than the H−H bond so the reaction must be endothermic." Evaluate this statement. Answer: Energy in = 436 + 242 = 678 kJ/mol. Energy out = 2 × 431 = 862 kJ/mol. ΔH = 678 − 862 = −184 kJ/mol (exothermic). The student's statement is incorrect because the overall energy change depends on ALL bonds broken and formed, not just one comparison. Although H−Cl is weaker than H−H, two H−Cl bonds are formed per molecul
Stretch & Challenge (Grade 8-9):
  • Synoptic links: explain how exothermic and endothermic reactions connects to another Chemistry topic you have studied
  • Real-world: research one real-world use or example of exothermic and endothermic reactions
  • Critical: "What are the limitations of the models used in exothermic and endothermic reactions?"

Plenary (5 minutes)

Assessment Criteria
  • Got it: Confident explanation + correct worked examples
  • Getting there: Main points OK, needs support with detail
  • Not yet: Confused on key concepts - re-run Lesson 2

Homework & Consolidation

Recommended Resources

🎓 Smart Lesson (Guided)