Hydrocarbons (u2a)

• Hydrocarbons are compounds which contain hydrogen and carbon.
• When enough oxygen is present, a hydrocarbon will burn to form carbon dioxide and water. This is called complete combustion. (Occurs in bunsen burner when the air hole is fully open, giving a blue flame).
• When there is not enough oxygen present, incomplete combustion occurs, incomplete combustion produces unburnt carbon (soot) and the poisonous gas carbon monoxide.
• The homologous series is a family of compounds with the same general formula and similar chemical properties.
• Alkanes have single bonds and are saturated compounds.
• Alkanes are insoluble in water and are commonly used as fuels
• Alkanes have a general formula of CnH2n+2.
• Alkenes and Cycloalkanes have a general formula of CnH2n
• Cycloaklanes begin with cyclopropane
• Cycloalkanes are saturated hydrocarbons
• Alkenes have a carbon to carbon double bond and are unsaturated.
• Alkenes are used to make polymers and alcohols
• The first alkene is ethene, which has the molecular formula C2H4
• Cycloalkanes are used to make fuels and solvents
• Isomers are compounds with the same molecular formula but different structural formula.
• Combustion is a chemical reaction where substances burn in the presence of oxygen
• An exothermic reaction is a chemical reaction that releases energy (heat)
• An endothermic reaction is a chemical reaction that absorb or take in energy (heat).
• Combustion is an example of an exothermic process.
• Hydrogenation is when alkenes react with hydrogen to form alkanes
• Alkenes react with halogens to form dihaloalkanes
• The test for unsaturation is a test to see if a molecule contains a double bond
• Test for unsaturation- If the molecule is unsaturated the bromine will turn from brown to colourless
• Hydration is when alkenes react with water to form alcohols
• An unsaturated hydrocarbon decolourises bromine water quickly
• Alkenes decolourise bromine solution quickly, but alkanes and cycloalkanes do not
• A monomer is a small molecule that joins together to make polymers
• A polymer is a large molecule that is made up of monomers
• Viscosity is a measure of the resistance of a substance flow. (the more thicker the substance is the more viscous it is).
• Thermal cracking is when large molecules are broken up by heat alone.
• Cracking: heating a large hydrocarbon which will then make smaller more useful products like petrol.
• Catalystic cracking: A process that breaks down long chain hydrocarbons into shorter ones
• Fractional distillation separates a mixture of liquids into two or more fractions