AQA A Level Chemistry : Year 1 - Alkanes with 100% correct answers

What is a source of hydrocarbons? Crude oil (petroleum) What is crude oil (petroleum) ? A mixture consisting mainly of alkane hydrocarbons which can be separated by fractional distillation 00:03 01:36 How might blockage of the air vents in a combustion engine affect its performance? Less energy given out by the fuel Engine less powerful/efficient What is fractional distillation? The continual evaporation and condensation of a mixture causing the different components to separate because they have different boiling points Explain fractional distillation (4 steps) 1. Crude oil is heated to a vapour which passes into the column 2. The column is hotter at the bottom and cooler at the top 3. Vapours rise up the column and cool, condensing when they meet their boiling point 4. Short chain alkanes are collected near the top as they have lower boiling points Give a use of alkanes Fuels What is an alkane? A saturated hydrocarbon What is cracking? The proceds where long chain hydrocarbon molecules are broken into shorter chain molecules which are in high demand What bond is broken during cracking? C-C Why are high temperatures needed in both thermal and catalytic cracking? The C-C bond is very strong Requires high amount of energy to break Why is it necessary to crack hydrocarbons? To produce short chain hydrocarbons which are in high demand What are the conditions for thermal cracking? 1200K 70 atm 1 second No catalyst What are the products of thermal cracking? High % of alkenes with some short chain alkanes What are the conditions for catalytic cracking? 800-1000K 1-2 atm 2-4 seconds Catalyst of aluminosilicate zeolite