Year 8 End-of-Year Revision: Chemical Reactions

What Are Chemical Reactions?

Ever wondered what actually happens when you burn toast or watch fireworks explode? You're witnessing chemical reactions in action! A chemical reaction occurs when substances called reactants rearrange their atoms to create completely new substances called products.

Think of it like rearranging LEGO blocks - you've got the same pieces, but they're connected differently to make something totally new. For example, when carbon burns in oxygen, it creates carbon dioxide: Carbon + Oxygen → Carbon dioxide.

Spotting chemical reactions is easier than you might think! Look out for colour changes, flames, temperature changes (getting hotter or colder), fizzing sounds, or new smells appearing. These are all telltale signs that atoms are busy rearranging themselves.

Key Difference: Chemical changes create different particles and can't be easily reversed (like cooking an egg), while physical changes keep the same particles and are reversible (like melting ice).

The most important thing to remember is whether energy is released or absorbed. Exothermic reactions release energy and get hot, whilst endothermic reactions absorb energy and get cold.

Fuels and Important Reaction Types

Fuels are basically energy storage devices that release power when they burn. Petrol, diesel, coal, and even cooking oil all store chemical energy that gets released during combustion (the scientific word for burning).

Every combustion reaction needs three things to work: fuel, heat, and oxygen. Remove any one of these, and the fire goes out! When methane burns, it combines with oxygen to make carbon dioxide and water - this is called an oxidation reaction.

Rusting is another type of oxidation that happens when iron meets oxygen in the air. It's basically very slow burning that creates iron oxide (rust) instead of flames.

Thermal decomposition sounds complicated, but it's just breaking things apart with heat. When you heat metal carbonates (compounds containing metal, carbon, and oxygen), they split into metal oxide and carbon dioxide gas.

Remember: All these reactions follow the same basic principle - atoms rearrange to form new substances, and energy either gets released or absorbed in the process.