Alkanes

Question 1

alkane general formula

Answer 1

CnH2n+2

Question 2

what is a hydrocarbon

Answer 2

a compound made of only hydrogen and carbon atoms

Question 3

saturated or unsaturated and why

Answer 3

alkanes and cycloalkanes are saturated hydrocarbons because they contain c-c single bonds

Question 4

general formula of a cycloalkane

Answer 4

CnH2n

Question 5

define heterolytic bond fission

Answer 5

when the bond breaks unevenly (one bonded atom gets both electrons)

Question 6

heterolytic bond fission arrows

Answer 6

X—– Y -> X+ + Y-
—>

Question 7

define homolytic bond fission

Answer 7

when the bond breaks evenly (both bonded atoms receive an electron)

Question 8

homolytic bond fission arrows

Answer 8

X—–Y -> X* + Y*
<—–>

Question 9

what is produced through homolytic bond fission and what are they

Answer 9

free radicals (very reactive species that have an unpaired electron)

Question 10

what type of reactions are reactions with halogens

Answer 10

photochemical reactions and radical substitution reactions

Question 11

define photochemical reaction

Answer 11

reaction that requires UV light

Question 12

why are reactions with halogens substitution

Answer 12

because hydrogen is substituted

Question 13

symbol equation for methane + chlorine

Answer 13

CH4 + Cl2 -> CH3Cl + HCl

Question 14

name and describe the three steps in reactions with halogens

Answer 14

1- initiation (radical produced)
2- propagation (radicals used up and created)
3- termination (radicals reacted together)

Question 15

methane + chlorine initiation

Answer 15

Cl2 –(UV) –> 2Cl*

Question 16

methane + chlorine propagation

Answer 16

Cl* + CH4 –> *CH3 + HCl
CH3 + Cl2 –> CH3Cl + Cl

Question 17

methane + chlorine termination

Answer 17

Cl* + Cl* –> Cl2
Cl* + *CH3 –> CH3Cl
*CH3 + *CH3 –> C2H6

Question 18

Limitations of radical substitution (carbon chain)

Answer 18

the reactions can occur anywhere along the carbon chain
structural isomers can form

Question 19

Limitations of radical substitution (too much chlorine)
- describe and show with symbol equations

Answer 19

Cl* + CH3Cl –> *CH2Cl + HCl
CH2Cl + Cl2 –> CH2Cl2 + Cl
with too much chlorine, the reaction continues forming dichloromethane, this continues with more sub-reactions
- forming trichloromethane, tetrachloromethane…

Question 20

how to solve limits of radical substitution- too much chlorine

Answer 20

solve with an excess of methane
- chlorine radical more likely to collide with methane and not chloromethane

Question 21

what is another name for crude oil

Answer 21

petroleum

Question 22

what is crude oil

Answer 22

a mixture of long-chained and short-chained hydrocarbons

Question 23

how can you separate crude oil

Answer 23

through fractional distillation

Question 24

describe the process of fractional distillation

Answer 24

• crude oil is vaporised at 350degrees celsius
• vaporised crude oil then placed in a fractionating column, it rises through the trays.
• the largest hydrocarbons remain at the bottom as ‘residue’ due to their boiling point being too high, they don’t vaporise
• each fraction condenses at their boiling point, the coolest being at the top
• separate fractions are collected
• hydrocarbons with the lowest boiling point don’t condense and are drawn off as gases at the top

Question 25

define cracking

Answer 25

breaking long-chained alkanes into smaller hydrocarbons

Question 26

cracking produces which two hydrocarbons

Answer 26

alkane + alkene

Question 27

what are the two types of cracking

Answer 27

thermal + catalytic

Question 28

conditions required for thermal cracking

Answer 28

1000degrees celsius, 70atm

Question 29

what is produced in thermal cracking

Answer 29

lots of alkenes which can become polymers

Question 30

conditions required for catalytic cracking

Answer 30

zeolite catalyst, 450degrees celsius, slight pressure

Question 31

what is produced in catalytic cracking

Answer 31

aromatics and motor fuels

Question 32

benefits of catalytic cracking

Answer 32

low costs as a low temperature and pressure required. catalyst speeds up reaction without being used up

Question 33

what is 'knocking'

Answer 33

when alkanes explode on their own accord when the fuel mixture in engines is compressed

Question 34

what type of hydrocarbons are most likely to knock

Answer 34

straight chained hydrocarbons

Question 35

how can you make knocking less likely and combustion more efficient and what is it called

Answer 35

convert straight chained hydrocarbons into branched/cyclic hydrocarbons (reforming)

Question 36

what is required for reforming and give an example

Answer 36

a catalyst (platinum stuck on aluminium oxide)

Question 37

reforming of hexane

Answer 37

hexane -> benzene (C6H6) + 4H2

Question 38

reformation of octane

Answer 38

2,5- dimethlyhexane

Question 39

name compounds produced by reforming

Answer 39

cycloalkanes, branched alkanes, arenes, aromatic hydrocarbons

Question 40

combustion of alkanes word equation

Answer 40

alkane + oxygen -> carbon dioxide + water

Question 41

what state must everything be in for combustion to take place

Answer 41

gas (vapour)

Question 42

word equation for incomplete combustion

Answer 42

alkane + oxygen --> carbon + carbon monoxide + water

Question 43

name pollutants produced from the combustion of alkane fuels

Answer 43

- carbon monoxide - oxides of nitrogen - sulfur dioxide - carbon particulates - unburnt hydrocarbons

Question 44

problems with carbon monoxide

Answer 44

- it is toxic - binds to haemoglobin in the blood - less oxygen is circulated around the body - victim dies of oxygen deprivation

Question 45

problems with sulfur dioxide

Answer 45

- burning fossil fuels that contain sulfur - sulfur dioxide gas enters atmosphere - dissolves in moisture, becomes sulfuric acid - creates acid rain

Question 46

problems with oxides of nitrogen

Answer 46

- in car engines, at high temperature and pressure oxygen and nitrogen react together - escapes into the atmosphere - dissolves in moisture, forming nitric acid - creates acid rain

Question 47

describe the harm created by acid rain

Answer 47

- destroys trees and vegetation - corrodes buildings and statues - kills fish in lakes

Question 48

describe the role of catalytic converters

Answer 48

to convert dangerous pollutants into harmless/less harmful gases

Question 49

what type of catalyst is used in a catalytic converter

Answer 49

platinum catalyst

Question 50

what can a catalytic converter turn the harmful gases into

Answer 50

carbon dioxide, nitrogen gas, water vapour

Question 51

give an example of a symbol equation for a catalytic converter

Question 52

define biofuels

Answer 52

fuels made from living matter over a short period of time

Question 53

name three types of biofuels

Answer 53

- bioethanol - biogas - biodiesel

Question 54

describe how bioethanol is made

Answer 54

ethanol is made from the fermentation of sugar from crop such as maize

Question 55

describe how biogas is made

Answer 55

from the breakdown of organic matter

Question 56

describe how biodiesel is made

Answer 56

from refining renewable fats and oils ( for example vegetable oils )

Question 57

why are biofuels seen as carbon neutral

Answer 57

they release carbon dioxide when burnt but the carbon dioxide has come originally from the plants during their growth

Question 58

which fuels are made from waste going to landfill

Answer 58

biodiesel and biogas

Question 59

name 3 problems with biofuels

Answer 59

- petrol car engines must be modified to handle fuels with high ethanol concentrations - land used to grow crops for fuel cant be used for food (problem in lic who rely on agriculture for their income) - CO2 is still produced through the farming, refining and transportation of the crops ( can't be completely classified as carbon neutral )