Alkanes

Question 1

give a description of alkanes

Answer 1

they are a homologous series of saturated hydrocarbons with the general formula CnH2n+2

Question 2

are alkanes reactive

however?

Answer 2

alkanes are very unreactive

however they burn in oxygen (combustion) and react with halogens to form halogenoalkanes

Question 3

what happens to BP of alkanes as chain length increases and why?

Answer 3

boiling point increase as chain length increases because greater surface area contact and therefore more van der waal forces between molecules

Question 4

what happens to BP as alkanes get more branched

Answer 4

BP decreases because they have less surface area contact between molecules and fewer van der waals forces between molecules

Question 5

what is crude oil

Answer 5

crude oil is a complex mixture consisting mainly of alkanes (including cycloalkanes) aromatic compounds and others containing S,O,N.

Question 6

is crude oil useful in its raw form ?

how does it become useful

Answer 6

no

by getting separated in fractional distillation

Question 7

what is distillation

Answer 7

distillation is a method to separate mixtures of miscible liquids where separation is based on boiling point

Question 8

list the essential features of fractional distillation of crude oil

Answer 8

1) crude oil is vaporised

2) the vapour is passed into a tower which is hotter at the bottom and cooler at the stop

3) as the vapour rises it cools

4) molecules will condense at different points as they have different boiling points

5) the larger the molecule the further down it condenses

6) this produces fractions ( a fraction is a mixture of hydrocarbons with similar boiling points

Question 9

the boiling point of the alkanes increases as the strength of the van der waal forces increases . this is increased bevause:

Answer 9

increased mr
increased surface area contact

Question 10

as the carbon chain gets longer, the hydrocarbons:

Answer 10

get more viscous

less flammable

less volatile

have higher BP

stronger van der waal forces between molecules

Question 11

how do we supply demand for shorter hydrocarbons

Answer 11

longer hydrocarbons are cracked

Question 12

what is cracking

Answer 12

cracking is the:

breaking of long chain alkane molecules into smaller ones

it involves breaking a strong C-C bond

Question 13

what is naptha

Answer 13

short chain hydrocarbons (C7-C14)

Question 14

why do we carry out cracking reactions

Answer 14

1) short chains are higher in demand economically

2) alkenes are used to make plastics and polymers

Question 15

what are the 2 types of cracking

Answer 15

thermal and catalytic

Question 16

describe thermal cracking

Answer 16

high temperature

high pressure

produces a high percentage of alkenes and straight chain alkanes

Question 17

describe catalytic cracking

Answer 17

high temperature

moderate presssure

zeolite catalyst

produces branched alkanes (motor fuels) , cycloalkanes and aromatic hydrocarbons

Question 18

why are alkanes used as fuels

Answer 18

they will burn

Question 19

what is complete combustion

Answer 19

alkanes reacting with excess of oxygen

Question 20

what is produced in complete combustion

Answer 20

alkane + oxygen —> carbon dioxide and water

Question 21

which is more exothermic complete or incomplete combustion

Answer 21

complete

Question 22

what’s incomplete combustion

Answer 22

reacting with limited oxygen

Question 23

what’s produced in incomplete combustion

Answer 23

carbon monoxide CO (toxic gas)

carbon C (black solid

Question 24

what’s produced in incomplete combustion

Answer 24

carbon monoxide CO (toxic gas)

carbon C (black solid)

and water

Question 25

what other pollutants are made in internal combustion engines

Answer 25

NO or NO2 unburnt hydrocarbons

Question 26

what other pollutants are made in coal burning power stations

Answer 26

SO2

Question 27

how do we reduce the problem of carbon monoxide

Answer 27

use catalytic converters in cars

Question 28

how do we reduce the problem of unburnt hydrocarbons

Answer 28

use catalytic converters in cars

Question 29

how do we reduce the problem of NO/NO2

Answer 29

use catalytic converters in cars

Question 30

what’s the problem with C carbon particulates

Answer 30

can cause respiratory problems

Question 31

what’s the problem with unburnt hydrocarbons

Answer 31

photochemical smog

Question 32

what’s the problem with NO/NO2

Answer 32

reacts with water to form acid rain

Question 33

how is NO NO2 formed

Answer 33

combustion of N2 in the air and O2 in the air at very high temperatures in engines and furnaces

Question 34

what’s the problem with sulfur dioxide

Answer 34

reacts with water to form acid rain

Question 35

how to reduce problem of SO2

Answer 35

flue gas desulfurisation

Question 36

what neutralises SO2

Answer 36

CaO and CaCO3 (bases)

Question 37

where are sulfur compounds found

Answer 37

in coal and crude oil

Question 38

how is SO2 formed

Answer 38

by burning of sulfur compounds

Question 39

why are high temperatures needed to produce NO2

Answer 39

to break the strong triple bond between nitrogen atoms

Question 40

name all the components of the catalytic converter

Answer 40

1) honey comb structure 2) made ceramic material 3) thin coating of metal catalyst ( rhodium palladium platinum)

Question 41

why honey comb structure

Answer 41

increase surface area and cost effective

Question 42

why ceramic material

Answer 42

withstands high temperatures of combustion engine

Question 43

why thin coating of metal catalyst ( rhodium platinum palladium)

Answer 43

to reduce cost and increase surface area

Question 44

what happens when dangerous gases pass over the catalyts give example

Answer 44

the dangerous gases react together to produce less harmful gasses 2CO + 2NO —> 2CO2 and N2

Question 45

give equation for formation of acid rain

Answer 45

4NO2 + 2H2O + O2 —> 4HNO3