ORGANIC CHEM - ALKANES + HALOGENOALKANES Flashcards
How is crude oil separated into fractions?
- crude oil vaporised
- crude oil rises up the column
- temp gradient in column (hotter at the bottom, cooler at the top)
- as the gas moves up the column, hydrocarbons condense at their boiling points
- boiling point depends on the size of the molecules (longer hydrocarbon chains have stronger van der waals forces so therefore higher boiling points)
- larger hydrocarbon chains condense at the bottom of the column while shorter hydrocarbon chains condense at the top
What is a fraction?
a mixture of hydrocarbon chains with similar boiling points
What is cracking?
breaking down longer hydrocarbon chains into smaller hydrocarbon chains as they are more useful
What conditions are required for thermal cracking?
- temp - 900°C
- pressure - 70 atm
- steam
- no catalyst
What are the products of thermal cracking?
alkenes
What are the conditions required for catalytic cracking?
- temp - 450°C
- pressure - 1-2 atm
- catalyst - zeolites
What are the products of catalytic cracking?
motor fuels (cyclic alkanes, branched alkanes, aromatics)
What are the products of complete combustion of an alkane?
CO2 and H2O
What are the products of incomplete combustion of an alkane?
CO/C (carbon particulates) and H2O
How is CO2 formed?
complete combustion
What problem(s) does CO2 cause?
global warming
How can the problem caused by CO2 be reduced?
burn less fossil fuels
How is CO formed?
incomplete combustion
What problem(s) does CO cause?
death
How can the problem caused by CO be reduced?
- burn substances in sufficient O2
- catalytic converters in cars
How are carbon particulates (C) formed?
incomplete combustion
What problem(s) do carbon particulates (C) cause?
- global dimming
- respiratory problems
How can the problem caused by carbon particulates (C) be reduced?
burn substances in sufficient O2
How is SO2 formed?
burning fuels
What problem(s) does SO2 cause?
acid rain
How can the problem caused by SO2 be reduced?
- can be removed from waste gases by flue gas desulfurization
- CaO + SO2 → CaSO3
How are nitrogen oxides (NOx) formed?
at high temps (eg: in car engines) N reacts O2 to NOx
What problem(s) do nitrogen oxides (NOx) cause?
- respiratory problems
- acid rain
- smog
How can the problem caused by nitrogen oxides (NOx) be reduced?
- catalytic converters in cars remove NOx
- 2NO + 2CO → N2 + 2CO2
What is free radical substitution?
a reaction mechanism where free radicals replace atoms in a molecule
What are the 3 main stages of free radical substitution?
- initiation
- propagation
- termination
What is the role of UV light in free radical substitution?
provides energy to break the bonds and generate free radicals
Nucleophilic substitution with OH:
- reagent?
- conditions?
- what happens?
- reagent: NaOH
- conditions: aq, warm
- what happens: halogen atom replaced by OH group
Nucleophilic substitution with CN:
- reagent?
- conditions?
- what happens?
- reagent: KCN
- conditions: aq ethanol, warm
- what happens: halogen atom replaced by CN group
Nucleophilic substitution with NH3:
- reagent?
- conditions?
- what happens?
- reagent: NH3
- conditions: excess concentrated NH3 dissolved in ethanol at pressure in sealed container
- what happens: 1st molecule of NH3 replaces halogen, 2nd molecule of NH3 removes H^+ from added NH3
Elimination of halogenoalkanes:
- reagent?
- conditions?
- what happens?
- reagent: KOH
- conditions: ethanolic (dissolved in ethanol), hot
- what happens: halogen atom and 1 H atom from adjacent C atom is removed giving an alkene (mixture of alkenes can be formed depending on which of the adjacent C atoms the H is lost from)
What are CFCs?
chlorofluorocarbons
What were CFCs used as?
- coolant in refrigerators
- propellent in aerosols
- degreaser for circuit boards
Whar is the ozone layer and what does it do?
- layer of O3 in the stratosphere
- absorbs UV radiation
What do CFCs do to the ozone layer?
- CFCs break down in the stratosphere to form Cl free radicals by the breaking of a C - Cl bond with energy from UV
- the Cl free radicals catalyse the destruction of ozone in a free radical chain reaction
- as CFCs went into large scale use, the conc of ozone in the ozone layer fell significantly
