8. Alkanes

Question 1

Alkanes Definition:

Answer 1

saturated hydrocarbon that contain only C-C and C-H single bonds

Question 2

Saturated Definitions:

Answer 2

compound contains only single bond

Question 3

Hydrocarbons Definition:

Answer 3

compounds containing only C and H

Question 4

What is the bpt of an alkane determined by?

Answer 4

• C-C chain length
• Number of branches (side chains)

Question 5

Why does the bpt of alkanes increase with chain length?

Answer 5

• have I.D.D foces between molecules
• strength of attraction increases with increasing size of molecule and number of e-
• longer the C chain, the bigger the molecule and the more e-

Question 6

Why does pentane have a higher bpt than 2,2-dimethylpropane?

Answer 6

• 2,2-dimethylpropane has more branches than pentane
• more surface contact between molecules of pentane
• induced dipole-dipole attractions between molecules of pentane are stronger

Question 7

Describe the essential features of fraction distillation that enables crude oil to be separated into fractions:

Answer 7

crude oil is heated to vaporise and enters the column
hydrocarbons have diff bpts that depend on their size/Mr/C chain length
column is cooler at the top, hotter at bottom
larger molecules iwth higher bpts condense at the bottom

Question 8

Thermal Cracking Conditions:

Answer 8

• high pressure
• high temperature

Question 9

Example: Thermal Cracking

1 mole of compound Y is cracked to produce 2 moles of ethene, 1 mole of but-1-ene and 1 mole of octane (C8H18). Deduce the molecular formula of Y.

Answer 9

C16H34 → 2 C2H4 + C4H8 + C8H18

Question 10

Catalytic Cracking Conditions:

Answer 10

• slight pressure
• high temperature (lower than thermal cracking)
• zeolite catalyst

Question 11

Equation for SO2(g) dissolving in O2 forming a very acidic solution of H2S04, known as acid rain:

Answer 11

SO2(g) + 0.5O2(g) + H2O (l) → H2SO4 (aq)

Question 12

Formation of Nitric Oxide (NO)

Answer 12

N2 (g) + O2 (g) → 2NO (g)

Question 13

Formation of Nitrogen Dioxide (NO2)

Answer 13

2NO (g) + O2 (g) → 2NO2 (g)

Question 14

Equation of NO2 dissolves in rainwater to produce an acidic solution (HNO3)

Answer 14

4NO2 (g) + 2H2O (l) +O2 (g) → 4HNO3 (aq)

Question 15

Flue Gas Desulphurisation

Equation for when a mixture of CaO and water is sprayed into the flue gas which reacts to form solid calcium sulphate

Answer 15

CaO (s) + 2H2O (l) + SO2 (g) + 0.5 O2 (g) → CaSO4.H2O (s)

Question 16

Flue Gas Desulphurisation

Equation for when flue gas is passed through CaCO3, producing calcium sulphate

Answer 16

CaCO3 (s) + 0.5 O2 (g) + SO2 (g) → CaSO4 (s) + CO2 (g)

Question 17

Catalytic Converter

Removal of CO and NO Equation

Catalytic Converters are made of platinum and thodium (are catalysts), honeycomb structure which increases S.A and rate of reaction

Answer 17

2NO (g) + 2CO(g) → N2 (g) + 2CO2 (g)

Question 18

Catalytic Converter

Removal of Unburnt Hydrocarbon and NO

Answer 18

C8H18 + 25NO → 8CO2 + 9H2O + 12.5N2