10.2 Functional group chemistry

Question 1

Combustion of alkanes and why they are used as fuels

Answer 1

Complete: C_nH_2n+2 + O₂ -> CO₂ + H₂O

Incomplete: C_nH_2n+2 + O₂ -> CO + H₂O

Extreme limitation of O2: C_nH_2n+2 + O₂ -> C + H₂O

Because:

highly exothermic because much E released in fomring double bonds in CO₂ and in H₂O

Question 2

Explain greenhouse gases

Answer 2

CO_² and H₂O (produced by combustion) are greenhouse gases - absorb infrared - contribute to global warming and climate change

Question 3

Explain global dimming

Answer 3

Unburned carbon released into air as small particles - form smog, affect respiratory system - contribute to global dimming

Global dimming: air pollution blocks sun’s rays - causes cooling effect

Question 4

Explain substitution

Answer 4

SUBSTITUTION: usually with saturated

Ex: halogenation in 3 steps

1. INITIATION: homolytic fission of halogen under UV
2. PROPAGATION: halogen radical attacks alkane - Hhal + alkane radical -> alkane radical reacts with another halogen radical - halogenalkane
3. TERMINATION: Two radicals combine: 2 halog radicals, 2 alkane radicals or halogen radical and alkane radical

Question 5

Explain addition reactions

Answer 5

Addition usually with unsaturated - alkenes - form different saturated products

Types of addition:

• hydrogenation (H)
• addition of halogens
• addition of halogen halides (HBr, HCl…)
• hydration (OH)
• addition polymerisation

Question 6

What could be synthesised from an alkene

Answer 6

Question 7

Combustion of alcohol

Answer 7

C_nH_2n+1OH + O₂ -> CO₂ + H₂O

Combustion = complete oxidation

Question 8

Oxidation of alcohols

Answer 8

Oxidising agent used (K₂Cr₂O₇) to increase bonds with O -> double bond - alcohol to aldehyde/carboxylic acid/ketone

Primary OH -> alhehyde -> carboxylic

Secondary OH -> ketone

Tertiary alcohols are not oxidised

Question 9

Explain reflux

Answer 9

Reflux - involves condensation of vapours into fractions according to boiling temp

Question 10

Explain esterification

Answer 10

Esterification - production of ester via condensation

alchol + carboxylic acid -conc. H₂SO₄-> ester

Question 11

Explain nucleophilic substitution

Answer 11

In halogenalkanes due to polarity - partial charges in molecules

Nucleophiles are attracted to e defficient C in halogenalkane - substitution of halogen occurs

Types of reactions:

• Sn1
• Sn2

Question 12

Explaine electrophilic substitution

Answer 12

usually with benzene - dense delocalised e ring - electrophiles are defficient in e - attaracted to the ring - replace H in benzene