6.4Chemistry 03. Changes To Materials

Know that some processes and reactions are endothermic or… — Cambridge Checkpoint Science 0893 Revision Notes & Topical Questions

5 min read 8 parts Lesson 4 of 9 1 quiz

📚 Cambridge Checkpoint Science 0893 Hub / Topical Revision

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Lesson summary

6.4 Exothermic and endothermic reactions and processes — CHECKPOINT - Lower Secondary Science 0893 notes: Know that some processes and reactions are endothermic or exothermic, and that this can be identified by a temperature change.Exothermic reaction — a chemical reaction in whi…

Energy transfer
Oxidation reaction
Reaction or process
Particles in melting
Insulation
Combustion

Part 1 of 6Exothermic reactions

Exothermic reaction

Exothermic reaction a chemical reaction in which thermal energy is given out to the surroundings.
The temperature of the surroundings rises.
Chemical energy stored in the substances is changed to thermal energy, and sometimes light and sound.

Energy transfer

Energy transfer the atoms rearrange into new combinations and chemical energy is changed to thermal energy that dissipates.

Part 2 of 6Examples of exothermic reactions

Reaction	Observation
Burning (combustion) of fuels such as wood, coal, gas and oil	Heat and light given out
Burning hydrogen to form water	Energy pushes a model rocket along a string
Burning magnesium to form magnesium oxide	Bright light and heat
Potassium with water	Hydrogen burns because of the heat
Magnesium with hydrochloric acid	The test tube gets hot
Calcium oxide with water	Heat is given off, used in self-heating cans

Oxidation reaction
- any reaction in which a substance combines with oxygen.

Part 3 of 6Endothermic reactions

Endothermic reaction

Endothermic reaction a reaction that takes in thermal energy from the surroundings.
Thermal energy is stored as chemical energy in bonds.
The temperature at the end is lower than at the start.

Example

Example sodium hydrogen carbonate + citric acid → sodium citrate + water + carbon dioxide
The test tube feels cool, as in sherbet sweets which give a cool fizzy feeling.

Part 4 of 6Endothermic processes

1Process

Process a change in which no new substance is made.
Potassium chloride dissolving in water cools the water.
Ice melting absorbs thermal energy from the surroundings.
Boiling and evaporation also take in thermal energy.

2Reaction or process

Reaction or process a reaction makes new substances, but a process such as dissolving or melting does not.

3Particles in melting

Particles in melting they absorb energy, vibrate more and overcome the forces holding them in place.

Part 5 of 6Comparison

Feature	Exothermic	Endothermic
Thermal energy	Given out to surroundings	Taken in from surroundings
Temperature of surroundings	Rises	Falls
Example	Burning	Sodium hydrogen carbonate with citric acid

Part 6 of 6Identifying by temperature change

Measure the starting temperature of the substances.
Mix them.
Measure the final temperature.
A rise shows exothermic and a fall shows endothermic.

Insulation
- a polystyrene cup reduces heat loss to the surroundings.

Key terms

Term	Meaning
Exothermic	Giving out thermal energy to the surroundings.
Endothermic	Taking in thermal energy from the surroundings.
Combustion	Burning.
Oxidation	A reaction in which a substance combines with oxygen.
Dissipate	To spread out into the surroundings.

Avoid these mistakes

Exothermic means energy is taken in — exothermic means energy is given out.

Energy is created in exothermic reactions — chemical energy is changed to thermal energy.

Dissolving is always a reaction — dissolving is a process because no new substance forms.

Endothermic reactions make the surroundings hot — they make the surroundings cooler.

Last updated: 12 October 2026