Year 10 Science · Unit 2 · Lesson 10
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Learning Goals
Read the energy diagrams
One energy profile diagram is shown below, for an exothermic reaction. Study it, then answer the three questions — the last one asks you to sketch the endothermic version yourself.
Diagram A, Exothermic reaction (e.g. combustion of methane)
(a) On Diagram A the green arrow marks the overall energy change, and the products line sits lower than the reactants line. The atoms are not destroyed, so the missing chemical energy has to have gone somewhere. Say where it went, and state what a thermometer left in the surroundings would read.
(b) The peak of the curve is the activation energy. Using bond breaking and bond forming, explain why a reaction that releases energy overall still has to have energy put in before it will start.
(c) Sketch how Diagram A would look different for an endothermic reaction. Describe the key change in one sentence.
Compare two
Complete the table to compare exothermic and endothermic reactions.
| Feature | Exothermic | Endothermic |
|---|---|---|
| Direction of energy flow | ||
| Effect on surrounding temperature | ||
| Energy of products vs reactants | ||
| Everyday Australian example | ||
| Industrial or practical application |
1. Eucalyptus oil has a very low flash point and is highly flammable. During the 2019 Blue Mountains bushfires, gum trees were observed to "explode" as volatile oils ignited. Using your knowledge of exothermic reactions and activation energy, explain what is happening chemically.
Wrap Up
In one sentence, what was the main idea of this lesson?