| Lesson Plan |
| Grade: |
Date: 25/02/2026 |
| Subject: Chemistry |
| Lesson Topic: State that the transfer of thermal energy during a reaction is called the enthalpy change, $Delta H$, of the reaction. $Delta H$ is negative for exothermic reactions and positive for endothermic reactions |
Learning Objective/s:
- State the definition of enthalpy change (ΔH) and its sign for exothermic and endothermic reactions.
- Explain how observed temperature changes indicate the sign of ΔH.
- Calculate ΔH using calorimetry data for a simple neutralisation reaction.
- Distinguish between heat transfer and heat production in chemical reactions.
- Apply the concept of ΔH to real‑world examples such as hand warmers and instant cold packs.
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Materials Needed:
- Projector and screen
- Whiteboard and markers
- Thermometers or digital temperature probes
- Simple calorimeter (polystyrene cup, stirrer)
- Samples: NaOH pellets, ammonium nitrate, dilute HCl and NaOH solutions
- Worksheets with reaction tables and calculation tasks
- Exit‑ticket cards
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Introduction:
Begin with a quick demonstration: place a hand warmer in a beaker of water and ask students what they feel. Recall that heat is energy transferred between a system and its surroundings, linking to prior lessons on temperature. Today they will identify the sign of ΔH for a reaction and explain why it occurs.
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Lesson Structure:
- Do‑now (5') – Students list everyday examples of hot and cold packs and share with the class.
- Mini‑lecture (10') – Define thermal energy, enthalpy change, and sign conventions; display an energy‑profile diagram.
- Guided inquiry (10') – Demonstrate dissolving NaOH (exothermic) and NH₄NO₃ (endothermic); students record temperature changes.
- Calorimetry calculation (10') – Using provided data, calculate q and ΔH for the neutralisation of HCl with NaOH.
- Concept check (5') – Quick quiz (e.g., Kahoot) on heat transfer vs heat production and sign of ΔH.
- Real‑world application (5') – Discuss hand warmers and instant cold packs; students write a sentence linking each to ΔH.
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Conclusion:
Summarise that ΔH reflects the direction of heat transfer, negative for exothermic and positive for endothermic reactions. For the exit ticket, each student writes the sign of ΔH for one of the demonstrated reactions. Homework: complete a worksheet calculating ΔH for a given neutralisation reaction.
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