Chem - Alkanes and Alkenes

what happens as the chain gets longer in a homologous series?

melting and boiling points rise
viscosity increases
flammability decreases

what is the functional group?

a functional group is the part of a molecule that largely dictates how the molecule will react
e.g. C=C bond (all alkenes have similar reactions because they have the same functional group), OH for alcohol and COOH for carboxylic acids

what are the key points about alkanes?

found in petroleum and natural gas
the first 4 alkanes are gas, next 12 are liquids and the rest are solids
saturated as they have single bonds
unreactive
used as fuels
lack of oxygen leads to incomplete combustion

what are structural isomers?

compounds that have the same molecular formula but different structural formulae

why do isomers have slightly difference properties

isomers have different structures
e.g. branched isomers have lower bp because the branches make it harder for the moleculars to get close leading to a weaker attraction further leading to lesser heat to overcome it

what is a photochemical reaction?

a reaction in which alkanes undergo substitution reaction with halogens in the presence of uv radiation where uv light provides activiation energy for this reaction

why are alkenes unsaturated?

they have double bonds

how can we distinguish between alkanes and alkenes?

by using a chemical test using bromine water (orange colored solution of bromine)
when bromine water is shaken with an alkane, it will remain as an orange solution as alkanes do not have double bonds
when bromine water is shaken with an alkene, the alkene will decolorise the bromine water and turn colorless as alkenes have double bonds
this reaction between alkenes and bromine is called an addition reaction

what is an addition reaction?

when 2 or more molecules react together to form only one product

what is a halogenation reaction?

an addition reaction where halogens are added to alkanes to form only one product

what is a hydrogenation reaction?

an addition reaction where hydrogen is added to alkenes to form an alkane which occur at 150 degrees using a nickel catalyst

what is a hydration reaction?

an addition reaction where steam is added to alkenes to form an alcohol which occurs at 300 degrees with a pressure of 60-70 atm using a concentrated phosphoric acid catalyst

what are the keypoints about alkenes?

made from alkanes by cracking
much more reactive than alkanes because the double bond can break to add on other atoms
adds on water as steam to form ethanol