3.2 Alkanes

Question 1

Crude oils

Answer 1

Mixture of hydrocarbons (mainly alkanes)

Remains of sea creatures and plants

Question 2

Fractional distillation of crude oil

Answer 2

1 mixture vaporised and enters fractioning column
2 has negative temp gradient
3 vapour rises cools and condenses at their bp
4 lighter bp condenses at top
5 each fraction useful for particular purposes
HIGHER DEMAND FOR SMALL FRACTIONS AS FEUL

Question 3

Thermal cracking

Answer 3

High temp high pressure
HOMOLYTIC FISSION (free radicals)
MAINLY ALKENES (principle product)

Question 4

Catalytic Cracking

Answer 4

ZEOLITE CATALYST lower pressure lower temp
HETROLYTIC FISSION (carbonation and carbanion)
BRANCHED ALKENES AND CYCLOALKENES (principle product)

Question 5

Cracking

Answer 5

Thermal decomposition of alkanes

Question 6

Properties of alkanes

Answer 6

NON POLAR (symmetrical distribution of charge)
Strongest intermolecular force is vdw
MORE LINEAR, MORE POINTS OF CONTACT, HIGHER BP

Question 7

Pollutants from alkane burning

Answer 7

CO
Nitrates (air reacts at high temps)
CO2
SO2 (sulphur impurities)
C (carbon particulates)
H2O

Question 8

Greenhouse gasses

Answer 8

CO2 AND H2O

Question 9

Acid rain

Answer 9

Nitrates and sulphur dioxide

SO2+½O2+H20 –> H2SO4

Question 10

Carbon particulates

Answer 10

Affects asthma, is carcinogen, global dimming

Question 11

Tetraethyl lead

Answer 11

In petrol, improves engine performance

Can accumulate in body tissue, damages nerve cells

Question 12

Catalytic converter

Answer 12

Stainless steel, honeycomb shape, RHODIUM CATAĹYST

2CO+2NO –>N2 +2CO2

Question 13

Flue gas desulpherisation

Answer 13

CaO+2H20+SO2+½O2–> CaSo4.2H2O

Question 14

RADICAL SUNSTITUTION

Answer 14

1) instigation of Cl2–>2Cl• using UV
2) propagation •Cl+CH4–>HCl+•CH3
Cl2+•CH3–> CH3Cl
(MULTIPLE SUBSTITUTION) use excess CH4
3) •Cl+CH3–> CH3Cl 2•CH3–>C2H6

OVERALL REACTION
CH4+Cl2–>CH3Cl+ HCl