Chemistry · Year 12

Active learning ideas

Enthalpy Changes: Exothermic & Endothermic

Active learning works for enthalpy changes because students need to touch the concept, not just see it. They must feel the warming of a calorimeter or puzzle through Hess’s Law calculations to grasp that energy is conserved in measurable ways.

• National Curriculum Attainment Targets
• A-Level: Chemistry - Enthalpy Changes
• A-Level: Chemistry - Exothermic and Endothermic Reactions

• 25–50 min
• Pairs → Whole Class
• 3 activities

Activity 01

• Inquiry Circle
• 50 min · Small Groups

Inquiry Circle: Fuel Efficiency Challenge

Groups use simple calorimetry to measure the enthalpy of combustion for different alcohols. They must then compare their results and discuss the sources of error, such as heat loss to the surroundings.

Differentiate between exothermic and endothermic reactions using energy profile diagrams.

Facilitation Tip

During the Fuel Efficiency Challenge, circulate with an infrared thermometer and ask groups to predict which fuel will cause the largest temperature rise before they begin.

What to look for

Provide students with two energy profile diagrams, one for an exothermic reaction and one for an endothermic reaction. Ask them to label the reactants, products, activation energy, and enthalpy change on each diagram and identify which diagram represents which type of reaction.

• Analyze
• Evaluate
• Create
• Self-Management
• Self-Awareness

Activity 02

• Think-Pair-Share
• 25 min · Pairs

Think-Pair-Share: Hess's Law Puzzles

Students are given a set of 'energy puzzle pieces' (enthalpy changes for various steps). They must work in pairs to arrange them into a Hess's Law cycle to find the enthalpy of a target reaction.

Explain the concept of standard enthalpy change of formation and combustion.

Facilitation Tip

In Hess’s Law Puzzles, require pairs to justify each step with bond energies before sharing with the class to build accountability.

What to look for

Present students with a list of chemical processes (e.g., combustion of methane, melting ice, respiration, photosynthesis). Ask them to classify each as either exothermic or endothermic and briefly justify their choice based on whether energy is released or absorbed.

• Understand
• Apply
• Analyze
• Self-Awareness
• Relationship Skills

Activity 03

• Stations Rotation
• 30 min · Small Groups

Stations Rotation: Enthalpy Definitions

Stations feature different chemical equations. Students must identify if the equation represents an enthalpy of formation, combustion, or neutralisation, and explain the 'standard conditions' required for each.

Analyze the energy changes involved in bond breaking and bond making.

Facilitation Tip

At the Enthalpy Definitions stations, have students rotate with a single shared notebook where each group must summarize key words in their own language before moving on.

What to look for

Pose the question: 'Why is it important to consider bond breaking as an endothermic process and bond making as an exothermic process when calculating the overall enthalpy change of a reaction?' Facilitate a class discussion where students explain the energy inputs and outputs involved.

• Remember
• Understand
• Apply
• Analyze
• Self-Management
• Relationship Skills

A few notes on teaching this unit

Teach enthalpy changes by starting with the physical experience of heat transfer before introducing abstract diagrams. Use calorimetry data to confront the temperature/heat misconception early, then layer in Hess’s Law as a problem-solving tool rather than a memorized rule. Research shows students grasp energy conservation better when they balance equations with real energy values they have measured themselves.

By the end of these activities, students will confidently distinguish between exothermic and endothermic processes, explain temperature vs. heat with real data, and apply Hess’s Law to calculate enthalpy changes they cannot measure directly.

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Watch Out for These Misconceptions

• During the Fuel Efficiency Challenge, watch for students who assume the fuel that burns fastest releases the most energy. Redirect by asking them to compare temperature changes per gram of fuel burned rather than total temperature rise.

  During the Station Rotation on Enthalpy Definitions, correct the idea that exothermic reactions always feel hot immediately by having students calculate expected temperature changes for 50 mL vs. 200 mL of water using the same energy release.

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Methods used in this brief

• Inquiry Circle
• Think-Pair-Share
• Stations Rotation