The four kinds
According to their nature, chemical changes can be divided into four types — and the four reactions of activity 16.2 are exactly those four.
1 — combination reactions
The first reaction of the activity: burning magnesium. Two substances combine into one.
2 — decomposition reactions
The second: heating potassium permanganate. One substance breaks into several.
3 — single displacement reactions
The third: zinc into copper sulphate solution. One element takes another's place.
4 — double displacement reactions
The fourth: barium chloride and sodium sulphate. Two compounds exchange parts.
Why sorting them matters
If you know which type a reaction belongs to, you can predict its products in advance. A combination has one product; a decomposition has one reactant; and in a displacement the pattern itself tells you what swaps with what.
Over the next six pages
We take each type in turn with its general form and its examples, then set all four side by side, and finish by sorting a handful of reactions.
The four types
Chemical reactions are of four types: combination, decomposition, single displacement and double displacement.