Energy Changes During Reactions
Science: KS3, topic 2.7.7
Energy Changes in Chemical Reactions
A chemical reaction happens when a substance undergoes a change into another substance. This requires energy.
Chemical reactions
- Substances that are at the start of chemical reactions are called reactants.
- The substances that are made at the end are called the products.
- All the atoms in a chemical reaction are conserved. This means they are not lost in the reaction.
- The mass of the reactants will always equal the mass of the products.
Exothermic reactions
- Exothermic reactions are reactions that give off heat to the surroundings.
- This causes the surroundings to get warmer.
- Examples of exothermic reactions include:
- Combustion (burning).
- Respiration.
- Neutralisation.
- Rusting.
Endothermic reactions
- Endothermic reactions are reactions that take in heat from the surroundings.
- This causes the surroundings to get cooler.
- Examples of endothermic reactions include:
- Photosynthesis.
- Cold packs.
- Evaporation of water.
- Melting ice.
- Thermal decomposition (when heat breaks down a substance into smaller parts).
Test yourself on Energy Changes During Reactions
Which of these is NOT an example of an exothermic reaction?
Which of these is NOT an example of an endothermic reaction?
Neutralisation is an example of an exothermic reaction. What happens to the temperature of the surroundings during a neutralisation reaction?
Select the correct statement about exothermic reactions