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10.3 Alkenes

10.3 Alkenes. 10.3.1 Describe, using equations, the reactions of alkenes with hydrogen and halogens. 10.3.2 Describe, using equations, the reactions of symmetrical alkenes with hydrogen halides and water. 10.3.3 Distinguish between alkanes and alkenes using bromine water.

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10.3 Alkenes

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  1. 10.3 Alkenes 10.3.1 Describe, using equations, the reactions of alkenes with hydrogen and halogens. 10.3.2 Describe, using equations, the reactions of symmetrical alkenes with hydrogen halides and water. 10.3.3 Distinguish between alkanes and alkenes using bromine water. 10.3.4 Outline the polymerization of alkenes. 10.3.5 Outline the economic importance of the reactions of alkenes.

  2. Alkenes • Unsaturated hydrocarbons containing a C=C bond. • A double bond is made of two different bonds, one sigma and one pi. • sp2 hybridized, so forming trigonal planar shapes (120o angles)

  3. Addition with halogens • React quickly at room temperature. • Accompanied by a loss of colour of reacting halogen. • This is often a test if alkenes are present. The brownish red Br2 will become colourless if an alkene is present.

  4. Addition with hydrogen • Hydrogenation occurs with a nickel catalyst at 150oC • Used to make margarine (solid version of oil) • Removing the C=C increases melting point, making oil compound solid at room temperature • Health wise = not good = trans fats

  5. Addition with hydrogen halides • Produce haloalkanes quickly at room temperature • HI>HBr>HCl reactivity order, because of bond strength.

  6. Addition with water • Hydration converts alkenes into alcohols using H2SO4 as a catalyst. • Economically important because ethanol is manufactured on a large scale as a solvent.

  7. Polymerization of alkenes • Alkenes can break their double bond and join each other to produce long chains called polymers. • The alkene that is used is called a monomer. • Major product in the organic industry: plastics, PVC • A very bad by-product is dioxin (linked to genetic disorder and cancers)

  8. References Addition with halogens: http://www.chemguide.co.uk/mechanisms/eladd/symbr2.html#top Hydrogenation: http://www.chemguide.co.uk/organicprops/alkenes/hydrogenation.html Addition with hydrogen halides: http://www.chemguide.co.uk/organicprops/alkenes/hhal.html Hydration: http://www.chemguide.co.uk/organicprops/alkenes/hydration.html Polymerization: http://www.chemguide.co.uk/organicprops/alkenes/polymerisation.html

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