C.12 Alkanes Flashcards
What are alkanes?
Saturated hydrocarbons; general formula, CnH2n+2
What does saturated hydrocarbon mean?
Each carbon atom has 4 bonds
What is a cycloalkane?
Functional group isomer of an alkane; general formula, CnH2n
What is crude oil?
Mixture of different length hydrocarbons
How does fractional distillation of crude oil work?
Crude oil placed in 350c furnace; Columns have temperature gradient, hottest bottom; longest chains don’t vapourise, shorter chains condense at higher fractions;
What are the types of cracking?
Thermal cracking, catalytic cracking
What is Thermal cracking?
Hydrocarbons are subjected to high heat and temperature to break molecular bonds and form shorter chains; mainly forms alkenes; High temperature and pressure (1000c, 70atm)
What is catalytic cracking?
Cracking with high temperature and zeolite catalyst, 450c; catalyst lowers cost and speed up reaction; products are mainly aromatic (contains benzene rings) hydrocarbons and fuels
How do alkanes combust?
Burn completely in O2; good fuel, burn readily producing large amounts of energy; Alkane + O2 = H2O + CO2
How does incomplete combustion occur with alkanes?
Burn with limited O2; Alkane + 1/2 O2 = H2O
+ CO
How is carbon monoxide harmful and how do you remove it?
Poisonous, bonds to haemoglobin in blood, prevents O2 bonding; remove using catalytic converter; soot causes breathing problems, make building dirty, clog up engines
What is global warming?
Gradual warming of the Earth; generally due to the greenhouse effect
What is increasing greenhouse gasses?
Human activities; burning fossil fuels; landfill
What is the process of greenhouse effect?
Electromagnetic radiation from Sun reaches Earth; absorbed by land and sea, re-emitted as infrared radiation; greenhouse gasses absorb IR radiation into covalent bonds; re-emit IR radiation back to earth warming it
What are the greenhouse gases?
CO2, H2O, CH4
What is photochemical smog?
Mixture of solid carbon particles & ozone
What does photochemical smog do?
harms respiratory system in animals; damages plants; toxic to humans
How is nitrogen oxide found in the air formed?
N and O2 reacting under high temperature and pressure in car engines
How do we reduce amount of unburnt hydrocarbons and nitrogen oxides in the air?
Catalytic converters
How do burning fossil fuels contribute to acid rain?
Sulfur impurity reacts with O2 in air when burnt, releasing sulfur dioxide, acidic gas reacts with H2O producing sulfuric acid; falls as acid rain ( does same)
What are the effects of acid rain?
Damages plants, kill fish, erosion of buildings
How do we remove SO2 from flue gases?
Wet scrubbing; alkali used to neutralise SO2 in flue gases; dissolving calcium carbonate or oxide in H2O, spray on acidic SO2 gas
What are the stages of free radical substitution?
Initiation, propagation, termination
What occurs in initiation?
Radicals produced using visible light or UV; photochemical reaction; photodissociation; bonds break equally forming 2 highly reactive radicals
Cl2 –-U.V–> 2Cl∙
What occurs in propagation?
Radicals react with non radicals; new radicals created , react with other non radicals; chain reaction
Cl∙ + CH4 –> ∙CH3 + HCl
∙CH3 + Cl2 –> CH3Cl + Cl∙
What occurs in termination?
2 radicals react, forming non radical; ends chain reaction
Cl∙ + ∙CH3 –> CH3Cl
∙CH3 + ∙CH3 –> C2H6
