2.3 Alkanes

What does saturated molecule mean

Hydrocarbon does not contain C=C bonds

General formula

CnH2n+2

No functional group - unreactive

Alkanes polarity

Non-polar- electro negativity of carbon and hydrogen similar- only van der waals

Alkanes boiling point

Increases as carbon chain length increases- increasing van der waals- more energy to release individuals molecules as gas,

short chains- gas, pentane - liquid

Branched alkanes- lower melting point as cannot pack together as closely as unbranched chains -van der waals not so effective

Aldehydes boiling point

Higher than alkanes as has permeant dipole dipole attractions

Solubility alkanes

Insoluble- water held. By hydrogen bonds much Stronger than van der waals forces between alkane molecules, alkanes mix with non-polar liquid e.g TOLUENE OR BENZO

Combustion reaction definition

The chemical reaction of fuels with oxygen, releasing heat and forming oxides

Hydrocarbon combustion general equation

Hydrocarbon + oxygen → carbon dioxide + water

Complete combustion- plentiful. Supply of oxygen

Incomplete combustion

Not all carbon atoms converted to CO2,

Carbon monoxide (toxic, poisonous, danger of running car engine in enclosed space ) or carbon (soot) produced

Incomplete supply of oxygen

Combustion equations order balance

E.g C4H10 + O2 → CO2 + H2O

C, H, O

C4H10+ 6.5O2 → 4CO2 + 5H2O

Combustion flames

More carbon - more orange sootier

E.g ethanol (52%carbon)- clean blue flame

Hexane(84% carbon) - smoky orange flame

Pollution from fossil fuels

Burning fossil fuels- greenhouse gasses e.g CO2 and acidic gases e.g sulfur dioxide (acid rain), nitrogen oxides.

Effects of increased greenhouse gases

• climate change

• raised sea levels/increased flooding of low-lying regions

• melting of polar icecaps

Effects of acid rain

• corrosion of limestone buildings/statues

• death of fish

• defoliation of trees..

Methods to limit production of greenhouse and acidic gases (URSU)

• Using catalytic convertors

• remove sulfur from fuels

• scrubbing emissions from power stations/factories

• using alkalis using renewables energies

Harmful combustion products from car exhausts

• Carbon monoxide, (CO) poisonous gas produced by incomplete combustion.

• Unburnt hydrocarbons, (CxHy) may also enter the atmosphere and these are significant greenhouse gases. contribute photochemical smog cause variety health problems.

• Oxides of nitrogen, (NO / NO2) acidic gases leading to acid rain.

Catalytic converters in cars function how

Remove toxic gases from exhaust emissions, contain honeycomb structure thin layer of platinum, palladium, rhodium

Harmful gases catalytic converters equations

2NO → N2 + 02 - reduction

2NO2 → N2 + 202 - reduction

2CO+ 02 → 2C02 - combustion

CxHy + (x + y/4)O2 → xCO2 + (y/2)H2O - combustion

Combine e.g 2CO + 2NO → N2 + 2CO2

Methane chlorine reaction in sunlight, EQUATIONS

CH4 + Cl2 → CH3Cl + HCI

Monochloromethane (a local anaesthetic)

CH3Cl + Cl2 → CH2Cl2 + HCI

Dichloromethane (paint stripper)

CH2Cl2 + Cl2 → CHCl3 + HCI

Trichloromethane (anaesthetic, solvent)

CHCl3 + Cl2 → CCl4 + HCI

Tetrachloromethane - -produced with excess chlorine (solvent used in dry cleaning)

Name of mechanism for Alkane-Primary Haloalkane

free radical photochemical substitution

Substitution definition

Replacing one atom or group with a different group or atom.

Radical definition and caused why

A radical is a particle with an unpaired electron. This unusual particle is brought about by UV light causing homolytic fission

What are steps for 'free radical photochemical/substitution!'

1. One initiation step: one molecule forms two radicals

2. Two propagation steps: a molecule and a radical form a molecule and a radical

3. Three termination steps: two radicals form a molecule

What are curly arrows used for in mechanism

Movement of electrons

Initiation step

Halogen molecule (uv light)→ radicals

Step 2 propagation

Molecule + radical → radical + molecule

Termination step 3

( 2 radicals → molecules)

Termination products

Small amount of ethane, attacked by free readicals