Alkanes

Question 1

what is an alkane

Answer 1

a saturated hydrocarbon containing only C-H bonds

Question 2

what is the general formula of an alkane

Answer 2

CnH2n + 2

Question 3

are alkane bonds polar and why/why not

Answer 3

nonpolar as the carbon and hydrogens have similar electronegative

Question 4

which intermolecular forces do they have and why

Answer 4

Van der Waals forces of attraction as the bonds are non polar

Question 5

are alkanes soluble in water and why

Answer 5

insoluble in water because hydrogen bonds in water are stronger than alkanes van der waals forces of attraction

Question 6

how reactive are alkanes

Answer 6

very unreactive

Question 7

which reactions do alkanes undergo

Answer 7

combustion and reaction with halogens

Question 8

what is crude oil, how is it formed and is it renawable

Answer 8

mixture of fractions with hydrocarbon of similar boiling points and properties

formed at high temperatures and pressures deep below the earths surface adn over millions of years and therefore is non-renewable

Question 9

name the fraction from high to low boiling point

Answer 9

Gases
Petrol
Naptha
Kerosone
diesel
oil
fuel oil
bitumen

Question 10

what is fractional distillation and how does it work

Answer 10

crude oil is heated and passed through a fractioning tower that has a heat gradient where it is cold at the top and hot at the bottom

vapours rise up the column and condense when the temperature is smaller than the boiling point

shortest chains condense at the top as they have the lowest boiling points

Question 11

what is fracking and how is it done

Answer 11

natural gas that is held within rock is drilled into and HCL and methanol is added to break up the rock and collect the gas

Question 12

what are the pros and cons of fracking

Answer 12

advantages:
- gas supply for many years
- reduces imported gas and electricity

disadvantages:
- chemical additives can pollute water
- can cause small earthquakes

Question 13

why are alkanes cracked

Answer 13

turn long chain alkanes which are not economically valuable and turns them into shorter chain alkanes and alkenes

Question 14

what are the conditions for thermal cracking

Answer 14

700-1200 K temperature

7000kPa pressure

Question 15

what is the intermediate for the reaction

Answer 15

free radicals

Question 16

what are the main products of thermal cracking

Answer 16

alkenes

Question 17

what are the conditions for catalytic cracking

Answer 17

lower temp of 720K

lower pressure just above atmospheric

zeolite catalysts with honeycomb structure to give large SA

Question 18

what are the main products of catalytic cracking

Answer 18

cycloalkanes, aromatic hydrocarbons and branches alkanes

Question 19

write an equations for the combustion of propane

Answer 19

C3H8 + 5O2 —-> 3CO2 + 4H2O

Question 20

what is a fuel

Answer 20

something which releases heat energy when combusted

Question 21

what are the five main fuels compromising of alkanes

Answer 21

methane, butane, propane, petrol and paraffin

Question 22

what is incomplete combustion and what products are formed in the case of alkanes

Answer 22

combustion in a limited supply of oxygen

it forms carbon monoxide and soot

Question 23

which types of hydrocarbons are most likely to undergo incomplete combustion

Answer 23

longer chains

Question 24

what is the environmental impact of carbon monoxide

Answer 24

toxic and poisonous

Question 25

what is the environmental impact of nitrogen oxides

Answer 25

forms nitric acid which causes acid rain and smog

Question 26

what is the environmental impact of sulphur impurities

Answer 26

form sulphuric acid and causes acid rain

Question 27

what is the environmental impact of soot

Answer 27

asthma, cracking and global dimming

Question 28

what is the environment impact of unburnt hydrocarbons

Answer 28

photochemical smog

Question 29

what is the environmental impact of carbon dioxide

Answer 29

global warming

Question 30

what is the environmental impact of water vapour

Answer 30

global warming

Question 31

what are flue gases

Answer 31

gases given out by power stations

Question 32

write two equations for two different ways of desulfurising flue gases

Answer 32

CaO + 2H2O + SO2 + 1/2O2 ----> CaSO4.2H2O CaCO3 + SO2 + 1/2O2 ---> CaSO4 + CO2

Question 33

what are catalytic converters made up of

Answer 33

ceramic honeycomb coated with platinum, palladium and rhodium metals

Question 34

what do catalytic converters catalyse

Answer 34

2CO + 2NO --> N2 + 2CO2 hydrocarbons + CO --> N2 + CO2 + H2O

Question 35

what are greenhouse gases

Answer 35

gases which trap infrared radiation

Question 36

what is the greenhouse effect

Answer 36

greenhouse gases trap infrared radiation in the atmosphere and the atmosphere heats up due to this

Question 37

define carbon neutral activities

Answer 37

activities that produce no net carbon dioxide emissions

Question 38

how are halogenoalkanes formed from alkanes

Answer 38

free radical substitution reaction

Question 39

what are the three stages by free radical substitution

Answer 39

1. initiation which is when the halogen bond breaks 2. propagation which is when the chain part of the reaction where products are formed by free radicals remain 3. termination where free radicals removed and stable products are formed

Question 40

what are the conditions needed for the formation of a free radical chlorine atom

Answer 40

presence of UV light

Question 41

write equations for the reaction of CH4 with Cl2

Answer 41

initiation: Cl2 ---> 2CL. propagation: Cl. + CH4 ---> HCL + CH3. CH3. + Cl2 ---> CH3Cl + Cl. termination: .CH3 + Cl. --> CH3Cl 2Cl. --> Cl2 .CH3 + .CH3 --> CH3CH3

Question 42

what is the ozone layers function

Answer 42

protects the earth from harmful exposure to too many UV rays

Question 43

how do CFCs break the ozone layer down

Answer 43

free radical substitution

Question 44

write an overall equation for the decomposition of ozone into oxygen

Answer 44

2O3 --> 3O2

Question 45

write the free radical substitutions equations to show how Cl free radicals catalyse the break down of O3

Answer 45

Cl2 --> 2Cl. Cl. + O3 ---> ClO. + O2 ClO. + O3 --> 2O2 + Cl.