Types of Chemical Reactions
Introduced| English |
|---|
| synthesis/ˈsɪnθəsɪs/ |
| decomposition/ˌdiːkɒmpəˈzɪʃn/ |
| combustion/kəmˈbʌstʃn/ |
Sorting reactions into families
- Countless reactions exist, but they fall into a few patterns.
- Two things join; one thing splits; partners swap.
- Spot the pattern and you can predict the products.
- A handful of families covers most of what you will see.
Joining and splitting
- Synthesis 化合反应 combines two things into one ($A + B \to AB$).
- Decomposition 分解反应 breaks one thing into parts ($AB \to A + B$).
- They are exact opposites.
$A + B \to AB$ is which type of reaction?
Two things combining into one is a synthesis.
$AB \to A + B$ is which type?
One compound breaking into parts is a decomposition.
Swapping partners
- Single replacement: one element kicks out another ($A + BC \to AC + B$).
- Double replacement: two compounds swap partners ($AB + CD \to AD + CB$).
- Precipitation and neutralization are double replacements.
Match each pattern to its reaction type.
Join, split, and swap are synthesis, decomposition, and double replacement.
A precipitation reaction, where two compounds swap partners, is a ____ replacement.
Two compounds exchanging ions is a double replacement.
Burning in oxygen
- Combustion 燃烧反应 is a fuel reacting with oxygen and releasing energy.
- A hydrocarbon burns to $\text{CO}_2$ and $\text{H}_2\text{O}$.
- It always needs $\text{O}_2$ and gives off heat.
Classify the reaction
Sort each equation by its reaction pattern.
Every combustion reaction requires...
Combustion is a fuel reacting with oxygen.
Classify $2\text{H}_2 + \text{O}_2 \to 2\text{H}_2\text{O}$.
- Two substances combine into one product, so it is a synthesis.
- It is also a combustion, since a fuel reacts with oxygen.
A single reaction can belong to more than one type.
Hydrogen burning is both synthesis and combustion.
Some reactions fit more than one family -- hydrogen burning is both synthesis and combustion, and that is fine. Look at the pattern of reactants and products, not just the names. And combustion always involves oxygen; with no $\text{O}_2$, it is not combustion.
Most reactions fall into families: synthesis (join into one), decomposition (split apart), single and double replacement (swap partners), and combustion (fuel plus oxygen). Recognize the pattern to predict products, and remember a reaction can belong to more than one family.