Organic Chemistry Equations
Complete equation reference for IGCSE Chemistry 0620 organic reactions: combustion, addition, substitution, polymerisation, and functional group reactions.
Published by IGCSEChemistry.com.my
Chemistry teaching team: K. S. Tan (15+ years teaching IGCSE Chemistry) and Ms Yash (10+ years teaching IGCSE Chemistry) and Ms Kartini (15+ years teaching IGCSE Chemistry).
Mapped to Cambridge IGCSE Chemistry 0620 (2026–2028). Last updated 2026-08-19.
This page collects the organic chemistry equations for 0620, organised by reaction type. Use alongside organic naming rules and the organic chemistry topic pages.
Combustion of hydrocarbons
Complete combustion (excess O2)
hydrocarbon + O2 -> CO2 + H2O (always exothermic)
| Compound | Equation |
|---|---|
| Methane | CH4 + 2O2 -> CO2 + 2H2O |
| Ethane | 2C2H6 + 7O2 -> 4CO2 + 6H2O |
| Propane | C3H8 + 5O2 -> 3CO2 + 4H2O |
| Ethene | C2H4 + 3O2 -> 2CO2 + 2H2O |
| Ethanol | C2H5OH + 3O2 -> 2CO2 + 3H2O |
Incomplete combustion (limited O2)
Products include CO (carbon monoxide) and/or C (soot/carbon) instead of CO2.
2CH4 + 3O2 -> 2CO + 4H2O
CH4 + O2 -> C + 2H2O
CO is a toxic gas — see incomplete combustion.
Reactions of alkenes
Alkenes have a C=C double bond, making them unsaturated and reactive via addition reactions.
Addition of bromine (test for unsaturation)
C2H4 + Br2 -> C2H4Br2 (1,2-dibromoethane)
Observation: bromine water is decolourised (orange to colourless). Alkanes do not decolourise bromine water.
Addition of hydrogen (hydrogenation)
C2H4 + H2 -> C2H6
Conditions: nickel catalyst, 150 C. Used industrially to harden vegetable oils into margarine.
Addition of steam (hydration)
C2H4 + H2O -> C2H5OH (ethanol)
Conditions: phosphoric acid catalyst (H3PO4), high temperature (~300 C), high pressure (60-70 atm).
This is the industrial method for producing ethanol.
Addition polymerisation
nC2H4 -> (-CH2-CH2-)n (poly(ethene))
The C=C double bond opens and monomers join in a long chain. No other product is formed. See addition polymerisation.
Reactions of alcohols
Combustion
C2H5OH + 3O2 -> 2CO2 + 3H2O
Ethanol burns with a clean blue flame. Used as a fuel.
Oxidation (by acidified potassium dichromate)
C2H5OH -> CH3COOH (ethanoic acid)
Observation: orange dichromate solution turns green (Cr2O7^2- reduced to Cr3+).
Fermentation
C6H12O6 -> 2C2H5OH + 2CO2
Conditions: yeast (biological catalyst/enzyme), warm temperature (~30-40 C), anaerobic (no air). See fermentation.
Ester formation
CH3COOH + C2H5OH ⇌ CH3COOC2H5 + H2O
Conditions: concentrated H2SO4 catalyst, warm. Product is ethyl ethanoate (an ester) — sweet/fruity smell.
Reactions of carboxylic acids
Carboxylic acids are weak acids. They react like inorganic acids but more slowly.
| Reaction | Example |
|---|---|
| + metal | 2CH3COOH + Mg -> (CH3COO)2Mg + H2 |
| + carbonate | 2CH3COOH + Na2CO3 -> 2CH3COONa + H2O + CO2 |
| + alcohol | See ester formation above |
Cracking
Large alkane -> smaller alkane + alkene
Example: C10H22 -> C8H18 + C2H4
Conditions: high temperature with a catalyst (catalytic cracking) or high temperature and pressure (thermal cracking).
Purpose: produces useful shorter-chain fuels and alkenes for making polymers.
Substitution reactions
Alkanes undergo substitution with halogens in UV light:
CH4 + Cl2 -> CH3Cl + HCl
Conditions: UV light. One H atom is replaced by one Cl atom.
Write the equation for the complete combustion of propane (C3H8). [2 marks]
- C3H8 + 5O2 -> 3CO2 + 4H2O [2] (1 mark for correct formulae, 1 mark for balancing)
Ethene reacts with steam to form ethanol. State the conditions and write the equation. [3 marks]
- C2H4 + H2O -> C2H5OH [1]
- Temperature: approximately 300 C [1]
- Catalyst: phosphoric acid (H3PO4) / high pressure [1]
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