| Lesson Plan |
| Grade: |
Date: 25/02/2026 |
| Subject: Chemistry |
| Lesson Topic: Describe the substitution reaction of alkanes with chlorine as a photochemical reaction, with ultraviolet light providing the activation energy, $E_{mathrm{a}}$, and draw the structural or displayed formulae of the products, limited to monosubstituti |
Learning Objective/s:
- Describe the photochemical chlorination mechanism of alkanes, including initiation, propagation, and termination steps.
- Explain how UV light supplies the activation energy $E_{\mathrm{a}}$ and generates chlorine radicals.
- Identify and draw the structural formulas of monosubstituted chlorinated products for alkanes up to pentane.
- Analyse factors that influence the reaction rate and selectivity (bond dissociation energy, Cl₂ concentration, light intensity, temperature).
- Apply appropriate safety precautions when handling chlorine gas and UV radiation in the laboratory.
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Materials Needed:
- Projector and screen
- Whiteboard and markers
- Printed worksheet with reaction tables and product structures
- Molecular model kits (alkanes and chlorinated products)
- UV lamp demonstration set (shielded)
- Safety goggles, lab coats, and access to a fume cupboard
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Introduction:
Begin with a striking image of a UV lamp and ask students how light can drive chemical change. Recall that alkanes are saturated hydrocarbons and that radicals are key to many organic reactions. State that by the end of the lesson they will be able to describe the chlorination mechanism and sketch the monosubstituted products.
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Lesson Structure:
- Do‑now (5'): Students list examples of reactions that require light energy.
- Mini‑lecture (10'): Present the photochemical chlorination mechanism with animated slides, highlighting initiation, propagation, and termination.
- Guided practice (12'): Work through the mechanism on the board for methane, prompting students to write each step.
- Model activity (10'): In pairs, use molecular kits to build methane, ethane, propane and then replace one H with Cl, drawing the displayed formulas on the worksheet.
- Factors discussion (8'): Small‑group analysis of how bond strength, Cl₂ concentration, light intensity, and temperature affect the reaction.
- Safety briefing (5'): Review hazards of chlorine gas and UV light; demonstrate proper PPE and fume cupboard use.
- Check for understanding (5'): Quick quiz (exit ticket) with three short questions on mechanism steps and product identification.
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Conclusion:
Summarise the three‑stage radical chain and the role of UV light as the energy source. Collect exit tickets to gauge mastery and assign a short homework: draw the chlorination products for butane and pentane, noting which carbon is most likely substituted. Remind students to review safety guidelines before any lab work.
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