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Alkanes
AQA A Level Chemistry
| Question | Answer |
|---|---|
| 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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