Year 10 Science · Unit 2 · Lesson 10

Energy Changes in Reactions

Foundation Worksheet

Name

Date

Class

Learning Goals

Define exothermic and endothermic reactions and describe the energy flow in each.
Explain the roles of bond breaking and bond forming in energy changes.
Classify common reactions as exothermic or endothermic.

Warm Up

Match each term to its definition

Draw a line connecting each term on the left to its correct definition on the right. Or write the matching letter next to each term.

Term	Your answer	Definition
Exothermic reaction		A. The minimum energy needed for a reaction to begin.
Endothermic reaction		B. The process of pulling atoms apart in existing bonds, this always requires energy input.
Activation energy		C. A reaction in which the products have more energy than the reactants; the surroundings cool down.
Enthalpy change		D. A reaction that releases energy (usually as heat) to its surroundings, raising the surrounding temperature.
Bond breaking		E. The overall difference in energy between reactants and products in a reaction.
Bond forming		F. The process of atoms joining together to make new bonds, this always releases energy.

Your Turn

Sort it!

Write each reaction from the pool into the correct category box: exothermic or endothermic.

Combustion of natural gas Photosynthesis in leaves Iron oxidation in hand warmers Dissolving NH₄NO₃ in a cold pack Neutralisation of an acid with a base Thermal decomposition of limestone (CaCO₃ → CaO + CO₂) Cellular respiration in muscle cells Cooking an egg (breaking down protein) An explosion (e.g. TNT detonating) Rusting of a steel fence

Exothermic

Endothermic

Show What You Know

1. Explain the difference between exothermic and endothermic reactions in terms of energy flow and the effect on surrounding temperature.

Recall 2 marks

2. In terms of bond breaking and bond forming, explain why a reaction releases energy overall (is exothermic).

Recall 2 marks

Wrap Up

In one sentence, what was the main idea of this lesson?