BRAINCAKEAlkanes
Revision notes for Alkanes in AQA Chemistry (7404). Read the start of any lesson here, then sign in free for the whole lesson, the R.E.C.I.P.E. recall steps and the quiz.
- General FormulaAlkanes are saturated hydrocarbons.
- Straight ChainsIn a straight-chain (unbranched) alkane, each carbon atom is joined to no more than two other carbon atoms.
- Branched ChainsIn a branched-chain alkane, at least one carbon atom is joined to three or four other carbon atoms, so side chains come off the main chain.
- Cyclic AlkanesCycloalkanes are saturated hydrocarbons in which the carbon atoms are joined in a ring.
- Naming AlkanesTo name an alkane, first find the longest continuous carbon chain.
- Structural IsomersStructural isomers of alkanes have the same molecular formula but different arrangements of the carbon chain.
- Physical PropertiesAlkanes are non-polar molecules because carbon and hydrogen have very similar electronegativities.
- Fractional Distillation of Crude OilCrude oil is a mixture consisting mainly of alkane hydrocarbons, with different chain lengths.
- FrackingFracking (hydraulic fracturing) is a method of extracting natural gas and oil trapped in shale rock deep underground.
- Thermal CrackingCracking is the breaking of C-C bonds in long-chain alkanes to form shorter, more useful molecules.
- catalytic CrackingCatalytic cracking breaks long-chain alkanes using a zeolite catalyst, a high temperature of about 450 °C and a slight pressure.
- CombustionAlkanes are used as fuels because they burn in oxygen, releasing a large amount of energy.
- Polluting the AtmosphereBurning fossil fuels in engines and power stations releases several pollutants into the atmosphere.
- Flue Gas DesulfurisationFlue gas desulfurisation removes sulfur dioxide from the waste gases (flue gases) of power stations before they are released, to reduce acid rain.
- Catalytic ConvertersCatalytic converters are fitted to car exhausts to remove carbon monoxide, nitrogen oxides and unburnt hydrocarbons.
- Greenhouse EffectThe Sun emits radiation, mainly visible and ultraviolet, which passes through the atmosphere and warms the Earth's surface.
- Carbon Neutral ActivitiesA carbon neutral activity has no overall annual carbon emissions to the atmosphere.
- Free-Radical SubstitutionAlkanes react with halogens such as chlorine in the presence of UV light.
- Further SubstitutionFree-radical substitution does not stop after one hydrogen has been replaced.
- Ozone LayerThe ozone layer is a region of the stratosphere containing ozone, O3.