Core Concepts (Target: 'S' Pass)

• Define: What is an exothermic reaction?

• Define: What is an endothermic reaction?

• Identify: Is the combustion (burning) of a candle an exothermic or endothermic process?

• Recall: What happens to the temperature of the surroundings during an exothermic reaction?

• List: Give one real-world example of an endothermic process.

• State: When heat is released in a reaction, are the products at a higher or lower energy level than the reactants?

Understanding & Application (Target: 'C' Pass)

• Explain: Photosynthesis is an endothermic process. Where does the energy for this reaction come from?

• Describe: A student mixes sodium hydroxide and hydrochloric acid and observes the beaker getting warm. Is this reaction endothermic or exothermic? Explain why.

• Apply: Draw a simple, labelled energy level diagram for an exothermic reaction, showing the relative energy of reactants and products.

• Explain: The reaction between quicklime (CaO) and water is highly exothermic. Why would it be dangerous to add a small amount of water to a large container of quicklime?

• Relate: When an instant cold pack containing ammonium nitrate and water is activated, the pack becomes cold. Explain this observation in terms of heat transfer between the reaction and the surroundings.

Analysis & Higher-Order Thinking (Target: 'B' / 'A' Pass)

• Justify: All combustion reactions are exothermic, yet a fuel like petrol does not start burning on its own. It needs a spark. Explain why this initial energy input is needed, even for a reaction that releases a large amount of energy.

• Analyse: In an experiment to measure the heat of neutralization, a student mixes 50 cm³ of an acid and 50 cm³ of a base. The temperature rises by 10 °C. What are two key assumptions made when calculating the heat change using the formula Q = mcθ?

• Synthesize: Compare the energy changes that occur during a chemical reaction (like combustion) with the energy changes that occur during a physical change (like melting ice). How are they different in terms of what the energy is used for?

• Apply: Design a simple experiment to determine whether dissolving solid potassium nitrate (KNO₃) in water is an endothermic or exothermic process. List the apparatus you would need and the steps you would take.

O/L Exam Tip: Be very clear on the definitions of exothermic (releases heat, surroundings get hotter) and endothermic (absorbs heat, surroundings get colder). You should be able to draw and interpret simple energy level diagrams for both types of reactions.