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Elias - Lusaka, ZambiaC$40
C$40Enthalpy Changes in Chemical Reactions; This lesson explores how chemical reactions involve energy changes that can be exo or endothermic.
Trusted teacher: Lesson Plan: Enthalpy Changes in Chemical Reactions Grade/Level: Secondary / IGCSE / AS level Duration: 60 minutes Topic: Enthalpy Changes in Reactions Lesson Objectives By the end of the lesson, students should be able to: 1. Understand that chemical reactions are accompanied by enthalpy changes, which can be exothermic or endothermic. 2. Construct and interpret reaction pathway diagrams, showing enthalpy change and activation energy. 3. Define and use key terms: standard conditions (⦵), enthalpy change of reaction (ΔHr⦵), formation (ΔHf⦵), combustion (ΔHc⦵), and neutralisation (ΔHneut⦵). Lesson Breakdown (60 minutes) 1. Introduction (5 minutes) Begin with a real-life hook: Ask: “Why does burning wood release heat, but dissolving ammonium nitrate in water feels cold?” Link to lesson: These are examples of exothermic and endothermic reactions. 2. Theory: Enthalpy Changes (10 minutes) Define enthalpy (H): The heat content of a system at constant pressure. Define enthalpy change (ΔH): Heat energy transferred during a reaction at constant pressure. Distinguish: Exothermic reaction: ΔH is negative (heat released). Endothermic reaction: ΔH is positive (heat absorbed). Give simple examples: Exothermic → combustion of methane. Endothermic → thermal decomposition of calcium carbonate. 3. Reaction Pathway Diagrams (15 minutes) Draw and explain two diagrams: Exothermic pathway: Products lower in energy than reactants, ΔH negative. Endothermic pathway: Products higher in energy than reactants, ΔH positive. Introduce activation energy (Ea):Minimum energy needed for reaction to occur. Label diagrams clearly: Reactants → peak (activation energy) → products. Highlight ΔH and Ea. 4. Standard Conditions and Key Enthalpy Terms (15 minutes) Explain standard conditions (⦵): 298 K (25°C), 101 kPa pressure, substances in standard states. Define and discuss: Standard enthalpy change of reaction (ΔHr⦵): Heat change when reaction occurs in molar quantities under standard conditions. Standard enthalpy of formation (ΔHf⦵): Heat change when 1 mole of compound is formed from its elements in their standard states. Standard enthalpy of combustion (ΔHc⦵):Heat change when 1 mole of substance is completely burnt in oxygen under standard conditions. Standard enthalpy of neutralisation (ΔHneut⦵): Heat change when an acid and alkali react to form 1 mole of water under standard conditions. Use simple examples for each (e.g., combustion of methane, formation of H2O, neutralisation of HCl with NaOH). 5. Guided Practice / Mini Activity (10 minutes) Students sketch their own reaction pathway diagrams (exothermic and endothermic). Label ΔH and Ea. Pair discussion: “Why do we still need activation energy even for exothermic reactions?” 6. Exercise (Homework / Classwork) (5 minutes) Answer the following questions: 1. State whether each reaction is exothermic or endothermic: a) Burning propane gas in oxygen. b) Photosynthesis in plants. c) Dissolving anhydrous copper(II) sulfate in water. 2. On a reaction pathway diagram: Show ΔH and Ea for an endothermic reaction. 3. Define the following terms and give one example each: a) Standard enthalpy of formation (ΔHf⦵) b) Standard enthalpy of combustion (ΔHc⦵) c) Standard enthalpy of neutralisation (ΔHneut⦵) 4. Under standard conditions, the enthalpy of combustion of methane is –890 kJ mol−1.
Chemistry
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