Alkanes Flashcards

What is a free radical?

A reactive species that possesses an unpaired electron and does not have a charge.

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What is a free radical?	A reactive species that possesses an unpaired electron and does not have a charge.
What are the conditions required for catalytic cracking?	Catalytic cracking requires high temperature (450°C) and slight or moderate pressure, along with a zeolite catalyst.
Describe the process of flue gas desulfurisation.	Flue gas desulfurisation is a process used to remove sulfur dioxide (SO2) from waste gases emitted from furnaces, such as coal-fired power stations. The gases pass through a scrubber containing basic calcium oxide (CaO), which reacts with the acidic sulfur dioxide in a neutralisation reaction to form calcium sulfite (CaSO3). The calcium sulfite can then be used to make calcium sulfate for plasterboard.
What are the environmental consequences of nitrogen oxides (NOx) pollution?	Nitrogen oxides (NOx) are toxic and can form acidic gases. They contribute to the formation of acid rain, which can have detrimental effects on ecosystems. Additionally, NOx can react with other pollutants in the atmosphere to form smog, which contributes to respiratory problems and reduces visibility.
What is the role of catalytic converters in reducing pollution from car exhaust gases?	Catalytic converters are devices that remove carbon monoxide (CO), nitrogen oxides (NOx), and unburned hydrocarbons from car exhaust gases. They contain a ceramic honeycomb coated with a thin layer of catalyst metals, such as platinum, palladium, and rhodium. These catalyst metals facilitate chemical reactions that convert harmful pollutants into 'harmless' carbon dioxide (CO2), nitrogen (N2), and water (H2O).
Define the greenhouse effect and its mechanism.	The greenhouse effect is the process by which certain gases in the Earth's atmosphere trap heat and warm the planet. UV wavelength radiation from the sun passes through the atmosphere and heats up the Earth's surface. The Earth then radiates out infrared long wavelength radiation. Greenhouse gases, such as carbon dioxide (CO2), absorb this infrared radiation, preventing it from escaping into space. The absorbed energy is transferred to other molecules in the atmosphere by collisions, resulting in the warming of the atmosphere.
How have carbon dioxide levels in the atmosphere increased in recent years?	Carbon dioxide levels in the atmosphere have risen significantly due to the increasing burning of fossil fuels. The combustion of fossil fuels, such as coal, oil, and natural gas, releases large amounts of carbon dioxide into the atmosphere, contributing to the greenhouse effect and global warming.
Describe the synthesis of halogenoalkanes.	Reaction of alkanes with bromine / chlorine in UV light to form a mixture of products with the halogens substituting hydrogen atoms.
Explain the process of initiation in the mechanism of halogenoalkane synthesis.	The UV light breaks the CI-CI bond, resulting in homolytic fission and the formation of chlorine free radicals.
What is the purpose of cracking larger hydrocarbons?	Cracking larger hydrocarbons allows for the utilization of excess larger hydrocarbons and meets the demand for shorter hydrocarbons.
How does propagation occur in the synthesis of halogenoalkanes?	Chlorine free radicals react with methane to form methyl free radicals, which then react with Cl2 to produce the main product and another Cl free radical.
What happens during the termination step in the mechanism of halogenoalkane synthesis?	Collision of two free radicals leads to the termination of the chain reaction.
Define homolytic fission.	The process of breaking a bond in such a way that each atom receives one electron from the covalent bond.
What is the purpose of UV light in the synthesis of halogenoalkanes?	UV light supplies the energy to break the CI-CI bond, initiating the reaction.
Describe the initiation step in the mechanism of bromine and propane reaction.	The initiation step involves the use of UV light to break the Br2 molecule into two Br radicals.
What is the propagation step in the mechanism of bromine and propane reaction?	The propagation step involves the reaction between the propane radical and a Br radical to form HBr and a new propane radical with a bromine atom attached.
Define termination in the mechanism of bromine and propane reaction.	Termination refers to the combination of two radicals to form a stable product, such as the combination of two propane radicals to form a propane molecule.
How does the presence of excess Cl2 promote further substitution reactions?	Excess Cl2 can react with the products of the initial substitution reaction, leading to further substitution and the formation of compounds like CH2Cl2, CHCl3, and CCl4.
What is the purpose of catalytic cracking?	Catalytic cracking is used to produce branched and cyclic alkanes, aromatic hydrocarbons, and sometimes hydrogen.
Describe the key points to learn about the fractional distillation of petroleum.	The fractions condense at different heights. The temperature of the column decreases upwards. The separation depends on boiling point. This is a physical process involving the splitting of weak van der Waals forces between molecules.
How does vacuum distillation work?	Lowering the pressure over a liquid will lower its boiling point. Vacuum distillation allows heavier fractions to be further separated without high temperatures which could break them down.
What is the purpose of a condenser in fractional distillation?	The condenser cools the vapours and condenses them into a liquid, which is then collected.
Define fractional distillation.	Fractional distillation is a process used to separate liquids with different boiling points by heating the mixture and collecting the vapors that condense at different heights in a fractionating column.
What is cracking?	Cracking is the conversion of large hydrocarbons to smaller hydrocarbon molecules by breaking C-C bonds.
What are the economic reasons for cracking?	The petroleum fractions with shorter carbon chains are in more demand than larger fractions.
Describe thermal cracking.	Thermal cracking is a type of cracking that requires high temperatures, high pressure, and produces mostly alkenes.
What are the products of complete combustion of alkanes?	The products of complete combustion of alkanes are carbon dioxide (CO2) and water (H2O).
Define incomplete combustion.	Incomplete combustion occurs when there is a limited amount of oxygen, producing carbon monoxide (CO) and/or carbon (C).
What is the process used to refine crude oil?	Fractional Distillation: Industrially
How does combustion of alkanes occur?	Alkanes readily burn in the presence of oxygen, resulting in highly exothermic combustion.
Describe the difference between complete and incomplete combustion.	Complete combustion produces carbon dioxide and water, while incomplete combustion produces carbon monoxide and/or carbon.
What are the two main types of cracking?	The two main types of cracking are thermal cracking and catalytic cracking.
What are the products of thermal cracking?	The products of thermal cracking are mostly alkenes, such as ethene used for making polymers and ethanol.
What are the conditions required for thermal cracking?	Thermal cracking requires high temperature (400°C to 900°C) and high pressure (7000 kPa).
What is the role of zeolite catalyst in catalytic cracking?	Zeolite catalyst is used in catalytic cracking to produce branched and cyclic alkanes, as well as aromatic hydrocarbons.
What is the potential environmental impact of incomplete combustion?	Incomplete combustion can produce carbon monoxide, which is toxic, and carbon (soot), which can cause global dimming by reflecting the sun's light.
What are the more valuable products obtained from cracking?	The products of cracking, such as ethene and branched alkanes, are more valuable than the starting materials.

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