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chemistry > 12 alkanes > Flashcards

12 alkanes Flashcards

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1
Q

define hydrocarbon

A

compounds containing carbon and hydrogen only

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2
Q

define saturated compounds

A

compounds containing single bonds only

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3
Q

define alkane

A

saturated hydrocarbons that contain only C-C and C-H single bonds

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4
Q

what is the general formula of an alkane?

A

C n H 2n+2

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5
Q

describe boiling points in alkanes

A

boiling points increase as carbon chain length increases
boiling points decrease when only branching increases
both affect induced dipole dipole forces

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6
Q

name a process for separating an alkane from a mixture of compounds

A

fractional distillation

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7
Q

outline the essential features of the fractional distillation of crude oil that enable the crude oil to be separated into fractions

A
  1. fractions have different boiling points
  2. depending on carbon chain length
  3. very hot at bottom of column and cooler at top
  4. longer molecules with higher bp condense at the bottom and smaller molecules with lower bp condense at the top
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8
Q

define fractions

A

mixtures of hydrocarbons with the same boiling point

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9
Q

what does cracking do?

A

converts long chain molecules into shorter chain molecules

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10
Q

why do oil companies need to crack heavy fractions?

A

smaller chain molecules are in higher demand

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11
Q

what are the two types of cracking?

A

thermal
catalytic

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12
Q

how does cracking convert long chain molecules into shorter chain molecules?

A

by breaking the C-C bonds

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13
Q

what do thermal and catalytic cracking produce high % of?

A

thermal: alkenes
catalytic: cycloalkanes and branched alkanes

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14
Q

give the conditions for thermal cracking

A

700-1200K
7000kPa

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15
Q

give the conditions for catalytic cracking

A

720K
100kPa
zeolite catayst

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16
Q

what is combustion in alkanes?

A

reaction with oxygen that releases energy

17
Q

what are the two types of combustion?

A

incomplete
complete

18
Q

give the conditions for both complete and incomplete combustion

A

complete: plentiful supply of oxygen
incomplete: limited supply of oxygen

19
Q

what does complete combustion form?

A

CO2 and H2O

20
Q

what does incomplete combustion form?

A

C or CO2 and H2O

21
Q

all hydrocarbon based fuels deriving from crude oil may produce pollutants when combusted. name the pollutants

A

CO2 (g)
H2O (l)
CO (g)
C (s)
SO2 (g)
oxides of nitrogen
unburnt hydrocarbons

22
Q

why is CO2 a pollutant?

A

causes global warming

23
Q

why is H2O (l) a pollutant?

A

is a greenhouse gas

24
Q

why is CO (g) a pollutant?

A

is toxic

25
Q

why is C (s) a pollutant?

A

can damage the lungs

26
Q

why is SO2 (g) a pollutant?

A

can form acid rain

27
Q

why are oxides of nitrogen pollutants?

A

can form acid rain

28
Q

why are unburnt hydrocarbons pollutants?

A

toxic and can cause cancer if inhaled

29
Q

what are two methods of reducing pollution?

A

flue gas desulfurisation
catalytic converters

30
Q

explain the two methods of desulfurisation

A
  1. CaO (s) + 2H2O (l) + SO2 (g) -> 0.5O2 -> CaSO4.2H2O (s)
  2. CaCO3 (s) + 0.5O2 (s) + SO2 (g) -> CaSO4 (s) + CO2 (g)
31
Q

what can calcium sulphate be used to make?

A

plaster for building

32
Q

what are catalytic coverters?

A

parts of modern car exhausts that convert harmful gases into less harmful ones

33
Q

what do catalytic converters look like?

A

honeycomb structure
made of platinum and rhodium metals

34
Q

why do catalytic converters have a honeycomb struture?

A

to increase surface area and rate of reaction

35
Q

what three harmful compounds do catalytic converters convert into less harmful compounds?

A

No
CO
unburnt hydrocarbons

36
Q

what is the equation for how catalytic converters convert NO and CO into less harmful gases?

A

2NO + 2CO -> 2CO2 + N2

37
Q

what are the products when catalytic converters convert NO and unburnt hydrocarbons into less harmful gases?

A

N2 CO2 and H2O

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