Types of Reactions
Core Concept
Synthesis: Two or more simple substances combine to form a single, more complex product (e.g., $A + B \rightarrow AB$).
Decomposition: A single compound breaks down into two or more simpler substances, usually requiring energy (e.g., $AB \rightarrow A + B$).
Single Replacement: One element trades places with another element in a compound, often involving a metal and an ionic solution.
Double Replacement: The cations and anions of two different compounds switch places to form two entirely new compounds.
Combustion: A hydrocarbon reacts rapidly with oxygen gas to produce carbon dioxide, water vapor, and heat.
Count the Products: If there is only one product, you are almost certainly looking at a synthesis reaction.
Check for Oxygen: Any reaction where $O_2$ is a standalone reactant and the products are $CO_2$ and $H_2O$ is a combustion reaction.
Watch the "Partners": In double replacement reactions, ensure you correctly pair the positive ion of the first reactant with the negative ion of the second.
Use an Activity Series: For single replacement reactions, verify that the standalone element is "strong" enough to displace the element currently in the compound.
Test Yourself
Podcast Episode
Practice Problems & Worked Out Examples 🔒
There are 5 major types of reactions that you might encounter.
Combination
Decomposition
Combustion
Single Replacement
Double Displacement
| Type | Format | Example |
|---|---|---|
| Combination (Synthesis) | $A + B \rightarrow AB$ | $2Mg(s) + O_2(g) \rightarrow 2MgO(s)$ |
| Decomposition | $AB \rightarrow A + B$ | $2H_2O(l) \xrightarrow{\text{electricity}} 2H_2(g) + O_2(g)$ |
| Combustion | Fuel $+ O_2 \rightarrow$ Oxides | $CH_4(g) + 2O_2(g) \rightarrow CO_2(g) + 2H_2O(g)$ |
| Single Replacement (Substitution) | $A + BC \rightarrow AC + B$ | $Zn(s) + CuSO_4(aq) \rightarrow ZnSO_4(aq) + Cu(s)$ |
| Double Displacement (Metathesis) | $AB + CD \rightarrow AD + CB$ | $AgNO_3(aq) + NaCl(aq) \rightarrow AgCl(s) + NaNO_3(aq)$ |