alkanes

Question 1

state 2 characteristics of homologous series

Answer 1

-differ by CH2
-have the same functional group
-chemically similar
-show a trend in physical properties

Question 2

saturated

Answer 2

only single bonds/ no double bonds

Question 3

equation for incomplete combustion of decane, C10H22, to produce carbon and water only

Answer 3

C10H22 + 11/2 O2 –> 11H2O + 10C

Question 4

equation for reaction between N and O to form nitrogen monoxide

Answer 4

N2 + O2 –> 2NO

Question 5

identify catalyst used in catalytic converter

Answer 5

platnium or rhodium

Question 6

write an equation for poisonous gas formed during the combustion of C16H34

Answer 6

C16H34 + 16.5O2 –> 16CO + 17H2O

Question 7

explain why the sulfur compounds found in crude oil should be removed from fractions before they are used for central heating fuel. (2)

Answer 7

SO2 is produced which causes acid rain

Question 8

equation to show hydrocarbon C16H34 being cracked to form C8H18, ethene and propene

Answer 8

C16H34–> C8H18 + C2H4 + 2C3H6

Question 9

equation for complete combustion of the alkane C11H24

Answer 9

C11H24 + 17O2 –> 11CO2 + 12H2O

Question 10

equation for the incomplete combustion of C11H24 to produce C and H2O only

Answer 10

C11H24 + 6O2 –> 12H2O + 11C

Question 11

equation for thermal cracking of 1 molecule of C10H22 to give one mole of propene and one mole of an alkane only

Answer 11

C10H22 –> C3H6 + C7H16

Question 12

why do the fractions collect at different levels in the fractionating column

(2)

Answer 12

temp decreases upwards

larger molecules condense at high temps/ lower down the column

Question 13

explain why it’s desirable that none of the sulphur-containing impurities naturally found in crude oil are present in petroleum fractions

Answer 13

sulphur burns to form SO2
S + O2 –> SO2
leading to acid rain

Question 14

the pollutant gas NO is found in the exhaust gases from petrol engines. Explain why NO is formed in petrol engines but it is not readily formed when petrol burns in the open air

(2)

Answer 14

NO formed by N2 and O2 from the air

high combustion temp provides enough energy to break N≡N

Question 15

explain how CO and NO are removed from the exhaust gases and why the removal of each is desirable

Answer 15

1) needs to remove NO as it forms acid rain/ toxic product / respiratory problems
2NO + O2 –> 2NO2
4NO2 + O2 + 2H2O –> 4HNO3

2) needs to remove CO as it’s poisonous

3) removed by catalytic converter
by catalyst platnium or rhodium -provide active sites

forms N2 + CO2
2NO + 2CO –> N2 + 2CO2

Question 16

incomplete combustion of dodecane to produce gaseous products only

Answer 16

C12H26 + 12.5O2 –> 12CO + 13H2O

Question 17

oxides of N are also produced during the combustion of paraffin in the air. Explain how these oxides of N are formed

Answer 17

nitrogen and oxygen react at high temps

Question 18

equation to show how nitrogen monoxide in the air is converted into nitrogen dioxide

Answer 18

2NO + O2 –> 2NO2

Question 19

equation to show how nitrogen dioxide reacts with oxygen and water to form nitric acid

Answer 19

4NO2 + 2H2O + O2 –> 4HNO3

Question 20

explain why the melting point of dodecane is higher than the mtp of the straight-chain alkane produced by cracking dodecane

Answer 20

longer carbon chain
stronger van der waal forces between molecules

Question 21

catalyst used in catalytic cracking

Answer 21

zeolite

Question 22

state and explain what happens to the yield of methanol when the total pressure is increased in this synthesis

CO2 (g) + 3H2 (g) ⇌ CH3OH (g) + H2O (g)

(3)

Answer 22

yield increases
more moles of reactants

equilibrium shifts from left to right to oppose the increase in pressure

Question 23

state and explain what happens to the yield of hydrogen in this reaction when temp is increased

CH4 (g) + H2O (g) ⇌ CO (g) + 3H2 (g)

(3)

Answer 23

yield increases
forward reaction is endothermic/ reverse is exo

equilibrium moves from (left to right) to oppose the increase in temp