Summary and Exam Tips for Alkenes
Alkenes is a subtopic of Organic Chemistry, which falls under the subject Science in the IB MYP curriculum. Alkenes are unsaturated hydrocarbons characterized by the presence of at least one carbon-carbon double bond (C=C), making them more reactive than alkanes. Their general formula is . Alkenes can be produced through cracking, a process where large alkane molecules are broken down into smaller, more useful molecules such as alkenes and hydrogen. This involves heating hydrocarbons to high temperatures (600-700°C) in the presence of a catalyst.
Alkenes can be distinguished from saturated hydrocarbons by their reaction with aqueous bromine. Unsaturated hydrocarbons will decolorize bromine water from orange to colorless, while saturated hydrocarbons will not react, leaving the solution orange. Alkenes undergo addition reactions, where the C=C double bond is broken to form a C-C single bond. Key reactions include bromination (forming dibromoalkanes), hydration (forming alcohols), and hydrogenation (forming alkanes). For example, ethene reacts with bromine to form 1,2-dibromoethane, with steam to form ethanol, and with hydrogen to form ethane.
Exam Tips
- Structural Formulas: Remember that only double and triple bonds are shown in structural formulas.
- General Formula: Be familiar with the general formula for each homologous series, such as for alkenes.
- Bond Types: Saturated compounds have single bonds only, while unsaturated compounds have double bonds.
- Bromine Water Test: Use the term colorless instead of clear when describing the reaction of bromine water with alkenes.
