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30 Cards in this Set
- Front
- Back
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Construct equations for complete combustion of cyclohexane |
C6H12+ 9O2 = 6CO2+ 6H2O Bold = balanced |
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Construct the equation for the complete combustion of cyclohexene |
C6H10+ 8.5O2 = 6CO2 + 5H2O |
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When alkenes and alkanes are combusted the flames produced look slightly different to each other suggest why this is? |
Alkenes have black smoke coming out of the flame because they are less saturated and don't completely combust |
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What would you expect the flame to look like of benzene C6H6 was combusted? |
Even more unsaturated so more black smoke |
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alkanes what group saturated or unsaturated bonding? reactive? burn? |
saturated (only single bonds) hydrocarbons -just carbons and hydrogens non polar-held together by weak van der waals forces pretty unreactive but burn well in suitable conditions |
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properties of alkanes-polarity |
non polar- electronegatives of hydrogen and carbon are very similar only forces are weak vans der waals they get stronger as the molecules grow in size |
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melting and boiling points of alkanes |
increased size means increased m&b points because the vans der waals forces increase with size by 18 carbons- alkanes are solid at room temp branched alkanes lower m&b point bigger surface area |
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solubility of alkanes |
not soluable in water because the hydrogen bonds in h2O molecules are stronger than the van der wals forces |
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reactivity of alkanes |
relatively unreactive due to strong c-c- c-h bonds they will burn/react with halogens in suitable conditions |
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crude oil = mixture of hydrocarbon chains - explain how they are seperated |
fractional distillation- hotter at the bottom longer chains cooler at the top shorter chains vapourised crude oil travels up the column and condenses in the fractions depending on their boiling point separating the different lengths |
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whats cracking and what problem does it solve |
breaks up the longer less useful (therefore less demanded) chains of hydrocarbons |
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thermal cracking |
high pressure high temp high proportion of alkenes good chemical feedstock for making polymers and plastics |
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catalytic cracking |
low pressure high temp=cheaper more branched alkanes presence of a zeolite catalyst can be reused good for petrol |
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combustion of alkanes -why? |
because they are unreactive therefore burnt to completion with sufficient oxygen release alot of energy (negative enthalpy) can be used to power machines |
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shorter alkanes when burnt |
release a large amount of energy when burnt as heat=good fuel |
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longer alkanes burnt |
in limited oxygen supply- combustion is not complete and carbon monoxide produced instead |
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environmental problems with using alkanes as fuels |
All hydrocarbon-based fuels produce polluting products when they burn, including carbon monoxide, carbon dioxide, nitrogen oxides, sulfur dioxide, carbon particles, water vapour and unburned hydrocarbons
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Nitrogen oxides and sulfur dioxide cause ....
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acid rain and photochemical smog.
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Carbon monoxide and carbon particles can...
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affect people’s health by acting as a poison, aggravating asthma, and causing cancer.
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Carbon dioxide, water vapour and unburnt hydrocarbons are greenhouse gases
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As greenhouse gases build up in the atmosphere, they reflect radiation (that would leave the atmosphere) back to the earth and cause it to warm.
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Flue gas desulfurisation and catalytic converters are used to reduce the impact of these products by preventing them entering the atmosphere....
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Flue gas desulfurisation extracts sulfur dioxide from the gases produced when burning fossil fuels in power stations.
Catalytic converters are attached to the exhausts of vehicles, they catalyse reactions with nitrogen oxides, carbon monoxide and unburnt hydrocarbons to make them into less harmful waste products before they are released into the atmosphere. |
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catalytic converter role |
gases converted to less harmful substances to make exhaust less polluting
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heterogeneous catalyst |
ceramic honeycombe structure coated in platinum and rhodium different physical state to reactants |
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how it increases the rate of reaction |
lower activation energy pathway from reactants to products |
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free radical substitution -initiation |
cl2 bond breaks making two free radicals |
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propogation type 1 |
hydrogen comes off methane forming hcl and ch3 free radical |
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propogation type 2 |
cl2 +free radical ch3= ch3cl + free radical cl |
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termination type 1 |
cl free radical and ch3 free radical form ch3cl |
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termination type 2 |
two ch3 free radicals make ethane or any alkanes |
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termination type three |
two cl free radicals form cl2 again |
