Organic reactions are the changes that carbon compounds undergo: burning, adding atoms across a double bond, oxidising an alcohol, joining an alcohol to an acid, and linking small molecules into long chains. They form a compact part of IGCSE Chemistry, and the same handful of patterns covers almost every question.
Questions usually ask you to write or complete an equation, name a product, or decide what an observation proves.
What should you know before starting?
You need to recognise a functional group and name small molecules, which organic families and naming builds. You also need to balance symbol equations, so formulas and equations is the key prerequisite, and the equation balance reasoning trainer gives quick practice.
Amount calculations appear in some questions, so relative masses and amounts helps.
An orienting example
Ethene, C₂H₄, has a carbon to carbon double bond. Add hydrogen across that bond and it becomes ethane: C₂H₄ + H₂ → C₂H₆. Add bromine and it becomes 1,2-dibromoethane: C₂H₄ + Br₂ → C₂H₄Br₂.
Count the atoms to check. Left side of the first equation: 2 C and 6 H. Right side: 2 C and 6 H.
The double bond has become a single bond, and each carbon has gained one atom.
Ethene also burns: C₂H₄ + 3O₂ → 2CO₂ + 2H₂O. Check: 2 C, 4 H and 6 O on each side. One molecule, two very different kinds of reaction.
In what order should you study the lessons?
- Explain combustion using products and evidence comes first, because every organic compound burns and the evidence tests are reused later.
- Represent addition to an unsaturated molecule shows what the double bond makes possible.
- Connect alcohol and acid transformations where in scope follows the chain from alcohol to carboxylic acid.
- Interpret an ester-forming relationship joins the alcohol and the acid you have just met.
- Recognise a polymer repeat unit from a monomer uses the addition idea again, repeated many times.
What are the common traps?
- Changing the number of atoms. An addition product must contain every atom of both reactants. Count before you move on.
- Keeping the double bond in a product. Once a molecule has added across the bond, that bond is single.
- Mixing up the names in an ester. The alcohol supplies the first word and the acid supplies the second.
- Treating a polymer repeat unit as a monomer. The repeat unit has no double bond in the chain.
- Reading an observation too far. A colour change or a gas test supports a conclusion, but only the one the evidence allows.
How should you use the practice set?
Work through the lessons in order, then try the organic reactions practice set with the answers covered. Write each equation in full before you open the worked answer.
Log the errors you make in the mistake log and retest queue so that you can retest the same pattern a week later with a fresh example.
Hazard notes in this module are there to explain why the chemistry behaves as it does. Laboratory work belongs with your teacher and your school or centre under proper supervision.
Students who follow the equations in class but freeze on a blank question often need someone to watch their reasoning live. That is the kind of work our teachers do in online one-to-one Chemistry tuition.