O- Alkanes

Question 1

What is the main source of alkanes?

Answer 1

crude oil

Question 2

Uses of alkanes

Answer 2

1. fuels
2. lubricants
3. starting materials for other compounds

Question 3

Bond angle of straight chain alkanes

Answer 3

109.5

Question 4

General formula for cyclic alkanes

Answer 4

CnH2n
** cyclic isomers to alkenes

Question 5

Polarity

Answer 5

non-polar
∵ C & H - similar electronegativities

Question 6

Boiling points

Answer 6

• longer chain ↑ bp
  –↑ vdW BETWEEN MOLECULES
• straight chain ↑ bp
  –√ packed ↑ tightly tgt–> ↑ vdW

Question 7

Solubility

Answer 7

• insoluble
  – strong H bonds in water, stronger than vdW between alkanes (↑ stable- x break to form vdW to mix)

Question 8

Reactivity

Answer 8

• unreactive ∵ strong C-C & C-H bonds

Question 9

3 conditions for crude oil to form

Answer 9

1. ↑↑ heat & pressure
2. millions of years
3. biomass (eg. plants & animals)

Question 10

What is crude oil?

Answer 10

Mixture of diff. (branched & unbranched) alkanes of diff. lengths

Question 11

What is a fraction?

Answer 11

Group of alkanes w/ similar chain lengths & bp

Question 12

What is bitumen used for?

Answer 12

1. road surfacing
2. further processed

Question 13

What are alkenes from fractional distillation used for?

Answer 13

1. polymers
2. starting materials for other compounds

Question 14

2 types of cracking

Answer 14

1. thermal
2. catalytic

Question 15

Conditions for thermal cracking

Answer 15

1. high temp- {700-1200K}
2. high pressure- {7000kPa}

Question 16

Describe how each type of products are formed in thermal cracking.

Answer 16

bond between 2 carbons in hydrocarbon chain splits into 2 molecules each w/ a free radical (unbonded e-)

Alkanes:
- free radical reacts w/ H –> alkane

Alkenes:
- x enough H –> loses 1 H–> alkene

Question 17

Conditions for catalytic cracking

Answer 17

1. lower temp- {720K}
2. ↓ pressure

Question 18

What is a zeolite catalyst + how is it adapted for its function?

Answer 18

• silicon dioxide + aluminium oxide
• honeycomb structure w/ ↑ s.a.
• acidic

Question 19

Types of products formed in catalytic cracking

Answer 19

1. branched alkanes
2. cyclic alkanes
3. aromatics

Question 20

What is the effect of no. of carbons in the amount of energy released in complete combustion?

Answer 20

↑ no. of carbons ↑ heat energy released

Question 21

Products of incomplete combustion

Answer 21

1. CO
2. carbon particulates (soot)

Question 22

As the chain length increases, what happens to the likelihood of incomplete combustion?

Answer 22

↑
∵ ↑ carbons require ↑ O2 for complete combustion

Question 23

How are Nitrogen oxides (NO, NO2, N2O4) formed?

What are the negative consequences?

Answer 23

• nitrogen & O2 from atmosphere react
• high temp
• ✔ react w/ water vapour & O2 in air–> nitric acid
  – 1. photochemical smog
  – 2. acid rain

Question 24

Negative consequences for CO

Answer 24

• toxic
• haemoglobin has a high affinity for it

Question 25

Negative consequences for carbon particulates

Answer 25

- cancer - exacerbate asthma

Question 26

Negative consequences of unburnt hydrocarbons

Answer 26

- photochemical smog

Question 27

Negative consequence of SO2

Answer 27

- sulfur in **fossil fuels**--> SO2 -- reacts w/ O2 & H2O in atmosphere --> sulfuric acid--> acid rain SO2 (g)+ 1/2 O2 (g) + H2O (l) --> H2SO4 (l)

Question 28

How is SO2 formed?

Answer 28

- sulfur-containing impurities in crude oil - sulfur in fossil fuels

Question 29

What is flue gas?

Answer 29

Fossil fuels burnt at power stations

Question 30

Describe how flue gas desulfurization is carried out

Answer 30

- 2 methods 1. spray slurry of lime (CaO) & water on flue gas --- SO2 forms calcium sulphite--> oxidised--> calcium sulfate (gypsum) * sold to make builder's plaster/ plasterboard CaO (s) + 2H2O (l) + SO2 (g) + ½ O2 (g) --> CaSO4.2H2O (s) 2. calcium carbonate xlime CaCO3 (s) + ½ O2 (g) + SO2 (g) --> CaSO4 (s) + CO2 (g)

Question 31

What does flue gas desulfurization get rid of?

Answer 31

sulfur dioxide

Question 32

What do catalytic converters get rid of?

Answer 32

- nitrogen oxides - carbon monoxide - unreacted hydrocarbons

Question 33

Describe what a catalytic converter is made of

Answer 33

- honeycomb structure - **ceramic** material - expensive metals eg. platinum & rhodium

Question 34

Important feature of a catalytic converter

Answer 34

↑ s.a. **↓ amount of metals for same effect**

Question 35

Chemical equation for removal of carbon monoxide

Answer 35

2CO (g) + 2NO (g)  N2 (g) + 2CO2 (g)

Question 36

Word equation for removal of unburnt hydrocarbons

Answer 36

Unreacted hydrocarbons + nitrogen oxide  nitrogen + carbon dioxide + water

Question 37

What is carbon neutrality?

Answer 37

- process/ activities that release no CO2 emissions overall

Question 38

What is the reaction forming a halogenoalkane called and what is the condition?

Answer 38

- substitution reaction- H substituted by halogen - condition- UV light

Question 39

3 steps in free radical substitution

Answer 39

1. initiation- halogen absorbs a single quantum of UV light 2. propagation- the chain part (repeats) 3. termination- getting rid of radicals

Question 40

Product of initiation

Answer 40

2 radicals eg. 2Cl.

Question 41

Why do C-H bonds not break under UV light?

Answer 41

wrong wavelength- only breaks bonds between halogens

Question 42

Products of each step in propagation

Answer 42

eg. reacting Cl w/ methane (CH4) 1. CH3 radical 2. Cl radical -- both reactants for the other reactions--> repeating chain

Question 43

Why are chain reactions not selective?

Answer 43

- any product can be formed - ∵ any C-H bond could be broken in alkane --> positional isomers

Question 44

List the 3 possible products in termination

Answer 44

👑 1. halogenoalkane 2. halogen 3. bigger alkane

Question 45

Why is a hole in the ozone (O3) layer a problem?

Answer 45

- harmful UV radiation from the sun goes through the hole - **sunburn + skin cancer**