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Alkanes

AQA A Level Chemistry

QuestionAnswer
What is an empirical formula? The simplest whole number ratio of atoms of each element in a compound
What is a molecular formula? The formula that shows the actual number of atoms of each element in a molecule
What is a general formula? A generalised formula which enables you to work out the molecular formula of a compound within a homologous series
What is a structural or shorthand formula? A formula showing the arrangement of atoms in a substance without showing the bonds. E.g. CH₃CH₂CH₃
What is a displayed formula? A formula showing the arrangement of atoms in a substance and all the bonds E.g.
What is a skeletal formula? A simplified version of a displayed formula where straight lines represent carbon-carbon bonds e.g.
What is a hydrocarbon? A compound made of atoms of hydrogen and carbon only
What is an alkane? A hydrocarbon with only single bonds.
What is chemical nomenclature? The process of naming different organic compounds
Name a given branched alkane Assign parent chain, assign branches a number and add as prefixes
What is isomerism? When molecules have the same atoms but they are arranged differently in space
What is structural isomerism? Where isomers have the same molecular formula but a different structure
What are the three types of structural isomerism? Chain, position and functional
What is a saturated hydrocarbon? A hydrocarbon with only single bonds
What is crude oil? A mixture of mainly alkanes that can be separated by fractional distillation
What is fractional distillation? The process of separating the alkanes in crude oil by use of their different melting points
What is cracking? The process of breaking C-C bonds in alkanes to make shorter molecules
What are the two types of cracking? Thermal cracking and catalytic cracking
How is thermal cracking carried out? At high pressure and temperature
What is thermal cracking used for? Producing a high percentage of alkenes
How is catalytic cracking carried out? Slight pressure, high temperature, zeolite catalyst
What is catalytic cracking used for? Production of motor fuels and aromatic hydrocarbons
Why is cracking carried out? The products of cracking are in greater demand than the long chain alkanes
What is combustion? The exothermic reaction of a fuel with oxygen
What is complete combustion? A combustion reaction where there is enough oxygen to ensure products are purely carbon dioxide and water
What is incomplete combustion? A combustion reaction where the lack of oxygen results in products other than carbon dioxide and water
What can the products of incomplete combustion be? Carbon monoxide, carbon
Which pollutants are produced by the internal combustion engine? Nitrogen oxides, carbon monoxide, carbon, unburned hydrocarbons
What is the purpose of a catalytic convertor? To remove gaseous pollutants produced by internal combustion engines
How is sulphur dioxide released from combustion engines? Through the combustion of hydrocarbons containing sulphur impurities
What is a flue gas? The gas released from large industrial plants and power plants
How can sulphur dioxide be removed from flue gases? By using calcium oxide or calcium carbonate to neutralise it
What is a free radical? A reactive species containing an unpaired electron
How are free radicals signaled? By use of a ∙ e.g.. Cl∙
How are chlorine free radicals produced? Exposure to UV light
What is free radical substitution? Where an atom bonded to a carbon is substituted for a free radical atom
Which steps are involved in a free radical substitution? Initiation, propagation, termination
What is an initiation step? The generation of a free radical
Give an example of an initiation step Cl₂ → 2Cl∙
What is a propagation? Intermediate steps in a free radical reaction which cause the regeneration of the original free radical
Give an example of a propagation CH₄ + Cl∙ → CH₃∙ + HCl, CH₃∙ + Cl₂ → CH₃Cl + Cl∙
What is a termination? A reaction involving two free radicals and resulting in no free radicals
Give an example of a termination CH₃∙ + Cl∙ → CH₃Cl
Why do free radical substitutions result in impure products Because there are many possible side reactions e.g. further substitution with chlorine or alkyl radical-radical reactions
Created by: JBearfield
 

 



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