2.1.2 Alkanes

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What is crude oil?
a source of hydrocarbons
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How is crude oil separated?
fractional distillation in a fractioning column // oil is heated to 350oC // heavier fractions with higher MP condense first and come off lower in the column // small come off at top
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What are the non-vaporisable hydrocarbons called?
bitumen
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Why do larger hydrocarbons have higher melting points?
more Van der Waal forces // larger surface area of contact so VdW stronger
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what is a fuel?
release heat energy when burnt
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describe the complete combustion of alkanes
highly exothermic// produces more energy when forming new bonds// produces water and co2
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where are alkanes used?
used as fuels in industry, home and transport
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what is the consequence of poor ventilation when an alkane is being burnt?
incomplete combustion can occur producing carbon monoxide
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Describe the incomplete combustion of alkanes
1/2 oxygen (O2) produces CO
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How is carbon monoxide toxic?
colour/odourless gas// binds with haemoglobin more readily that oxygen// suffocation
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What is the formula for alkanes?
CnH2n+2
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what are cycloalkanes?
ring shaped -2H
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describe the shape and bond angle of alkanes
bond angle 109.5// tetrahedral // all bonding pairs repel equally
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why are alkanes un-reactive?
C-C and C-H bonds are non-polar
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Describe the intermolecular forces between hydrocarbons
Van der Waal's only
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What is meant by the 'cracking' of hydrocarbons?
conversion of long chain H.carbons into smaller molecules by breakage of C-C bonds
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Why are hydrocarbons cracked?
long chain H.carbons are not very useful// cracked to produce smaller more useful
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What are the economic reasons behind cracking?
short chain H.carbons make petrol which is high in demand// supply demand for shorter// make use of excess larger molecules// products more valuable than reactants
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Describe hydrocarbons as fuels
non-renewable // over reliance is causing energy crisis// need to develop alternatives // increased CO2 emissions// global warming// climate change // political problems
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What are the conditions of catalytic cracking?
low Pa// temp 450oC // zeolite catalyst
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Why are high temperatures required in cracking?
strong covalent bonds need to be split
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What does catalytic cracking do and why?
turns straight chain alkanes into branched cycloalkanes and aromatic H.carbons // burn cleanly and have higher octane numbers
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What do good fuels have high octane numbers?
lower octane fuels ignite more easily which can damage engines
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How are straight chain hydrocarbons processed into branched/cyclic hydrocarbons?
by isomerism and reformation // isomerism - heat with catalyst and stuck on inert AlO // reformation - heat with palladium alloy catalyst and inert AlO
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Card 2

Front

How is crude oil separated?

Back

fractional distillation in a fractioning column // oil is heated to 350oC // heavier fractions with higher MP condense first and come off lower in the column // small come off at top

Card 3

Front

What are the non-vaporisable hydrocarbons called?

Back

Preview of the front of card 3

Card 4

Front

Why do larger hydrocarbons have higher melting points?

Back

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Card 5

Front

what is a fuel?

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