3.2 Alkanes

Question 1

What is crude oil

Answer 1

• made of alkanes, alkenes and aromatics (cycloalkanes)

Question 2

What happens to the boiling point of alkanes when carbon chain length increases

Answer 2

• increases
• in straight chain alkanes, the particles are packed closer together so there are greater intermolecular Van Der Waals forces.
• this requires more energy to overcome so BP increase

Question 3

Describe fractional distillation

Answer 3

• crude oil is heated until evaporation
• pumper into froactionating column which has a negative temperature gradient
• fractions rises until they get to a temperature where they condense
• fractions are collected and purified

Question 4

What is cracking?

Answer 4

The process of breaking down long chain hydrocarbons into more useful cohort chain alkanes and alkenes ( involves breaking down strong covalent bonds which requires a lot of energy

Question 5

What are the two types of cracking, the conditions and products

Answer 5

THERMAL CRACKING : 450 - 900°c and ~70 atm
Can from alkenes and some alkanes
CATALYTIV CRAKCING : 450°c and zeolite catalyst and ~1-2 atm
Forms branched alkanes and alkenes and cyclic and aromatic hydrocarbons

Question 6

Give the equations for complete and incomplete combustion

Answer 6

Complete (occurs in good oxygen supply)
Fuel + oxygen —> carbon dioxide and water
Incomplete
Flue + oxygen —> carbon monoxide (or just carbon) + water

Question 7

Describe global warming

Answer 7

Short wave length thermal radiation enters the atmosphere through the greenhouse gasses. It is absorbed and reemitted as long wavelength radiation which is trapped by the greenhouse gasses. Causes the overall increase of surface temperature of the earth

Question 8

Write the equations responsible for the depletion of the ozone layer

Answer 8

Cl* + O3 —> *ClO + O2
ClO.+ O3 —> Cl + 202
OVERALL
2O3 —> 3O2

Question 9

What is global warming?

Answer 9

Gradual increase of the overall temp of the earths atmosphere, attributed to the greenhouse effect

Question 10

What causes acid rain?

Answer 10

Nitrogen oxides - in the very high temps of the engine of a car, nitrogen reacts with oxygen
N2(g) + O2(g) —> 2NO(g)
2NO(g) + O2(g) —> 2NO2 (g)

Question 11

What is a catalyst and how does it work?

Answer 11

A substance that speeds up the rate of reaction without being used
-provides an alternative pathway to the reaction with a lower activation energy

Question 12

What is a catalytic converter

Answer 12

• converts toxic chemical gasses produced by the engine of the car into less harmful gasses
• plated in platinum, rhodium, palladium and NEEDS high temp
  2NO(g) —> N2(g) + O2(g)
  CO(g) + 1/2O2(g) —> CO2(g)