Alkanes

Question 1

What is the gen formula of alkanes?

Answer 1

CnH2n+2

Question 2

Hydrocarbon

Answer 2

compound cont C and H2 only

Question 3

Saturated

Answer 3

they cont no C=C or C—C bonds

Question 4

What is the trend with bp in alkanes?

Answer 4

As mol have more C atoms, bp increases

Question 5

What are the forces of attraction between neighbouring mol in alkanes?

Answer 5

Non-polar and only vdwF

Question 6

Why does bp increase as chain l increases?

Answer 6

vdwF forces of attr between the mol increases

Question 7

What happens to bp as branching increases? Why?

Answer 7

The higher the branching in the mol the lower the bp. More branching results in less vdwF between the mol b/c mol cannot pack as close together

Question 8

What is combustion?

Answer 8

Chem r of fuels with oxygen releasing heat and forming oxides

Question 9

Whats the trend in relation to hydrocarbons and their ignition?

Answer 9

Hydrocarb bec harder to ignite as mol get bigger b/c bigger mol don’t vaporise so easily
Bigger mol have greater vdw attr which makes it more dif for them to break away from their neighbour and turn into gas

Question 10

What colour is the flame the bigger the hydrocarbon?

Answer 10

Comb tends to be < complete as no C atoms in mol increases
Bigger the hydr the more likely you are to get a yellow, smoky flame

Question 11

What colour is flame in compounds with low C?

Answer 11

Blue clean flame

Question 12

Incomplete Combustion

Answer 12

where there isnt enougb O2 present can lead to form of C or CO

Question 13

What indicates inc comb?

Answer 13

Sooty flame

Question 14

What does burning fuels release?

Answer 14

Greenhouse gases

Question 15

Give e.g of greenhouse gases:

Answer 15

CO2, SO2 AND NO/NO2

Question 16

How do we reduce air pollution?

Answer 16

Removing s from fuels B4 combustion
Using catalytic converters in cars
Scrubbing emissions (with alkali) from power stations and factories
Using renewable en sources- e.g wind,wave,solar,hydroelectric and tidal

Question 17

What is the gh effect?

Answer 17

Co2 making up 0.03%-0.04% of atmosphere

Question 18

What are the conseq of the gh effect?

Answer 18

Climate Change
Raised sea levels
Melting of polar ice caps

Question 19

What is acid rain?

Answer 19

Acidic gases dissolving into water in env

Question 20

What is the conseq of acid rain on the env?

Answer 20

Corrosion of limestone features, statues and buildings
Death of fish in lakes and rivers
Defoliation of trees

Question 21

What do catalytic converters do?

Answer 21

Change poisonous mol like CO and various NOs in car exhausts into more harmless mol like CO2/N2

Question 22

How are the metals deposited? How does this act as an adaptation?

Answer 22

Metals deposited in thin layers onto a ceramic honeycomb
This max sa and keeps amount of metal used to a min b/c its v expensive

Question 23

What is catalytic poisoning?

Answer 23

When metal i.e lead coats honeycomb of expensive metals and stops it working

Question 24

What is the mechanism and conditions for monohalogenation of alkanes?

Answer 24

Free radical photochemical substitution
Under UV light

Question 25

Inititation R

Answer 25

Molecule -> Radicals

Question 26

Initation R for CL2

Answer 26

CL2 -> 2Cl’ (dot= radical)

Question 27

Propagation R

Answer 27

Molecule + Radical -> Radical + Molecule

Question 28

Write prop r for chlorine and methane:

Answer 28

CH4 + CL’ -> CH3’ + HCl
CH3’ + CL2 -> CH3CL + CL’

Question 29

Termination R

Answer 29

2 radicals -> Molecule

Question 30

Write 3 poss term r for chlorine and methane

Answer 30

Cl’ + Cl’ -> CL2
Ch3Cl’ + Cl’ -> Ch3Cl
CH3’ + CH3’ -> C2H6