Intro to organic Chem and Alkanes AQA A Level Chemistry

define empirical formula

the simplest ratio of atoms of elements in a compound

define molecular formula

the actual number of atoms of elements in a compound

define functional group

a group of atoms in a molecule that define a compound’s chemical reactions

define homologous series

a series of compounds with the same functional group and similar chemical properties

define structural isomerism

same molecular formula, different structural formula

what are the different types of structural isomerism?

• chain

• positional

• functional group

what is chain isomerism?

making branches

what is positional isomerism?

moving the functional group to a different carbon

what is functional group isomerism?

same molecular formula, different functional group

define stereoisomerism

same structural formula, different arrangement in 3D space

what are the requirements for a compound to have stereoisomers?

• contains a C=C which restricts rotation

• each C of C=C is attached to two different groups

what is the notation for stereoisomerism?

• E → priority groups on opposite sides

• Z → priority groups on same sides

what determines what a priority group is in stereoisomerism?

• go backwards with atoms bonded

• atom with highest Ar makes that group a priority

what is the general formula for alkanes?

CnH2n+2

what is a hydrocarbon?

compound containing only hydrogen and carbon

what is crude oil?

mixture of around 150 hydrocarbons, mainly straight chain alkanes

list the fractions of crude oil and their functions

• refinery gases - fuel for domestic heating and cooking

• petrol - fuel for cars

• naptha - used for chemicals

• kerosene - jet fuel

• diesel - for diesel engines

• lubricating oil - oil for cars

• fuel oil - fuel for ships

• bitumen - road surfacing

why do the boiling points of alkanes increase as chain length increases?

• higher Mr

• more van der waals form as more electrons

• require more energy to overcome

why do branched chain alkanes have lower boiling points than straight chain alkanes?

• branched chain means that the molecules have less surface area in contact with each other and are less compact

• less VDW

• require less energy to overcome

why are short chain alkanes useful?

clean fuels

how does chain length affect how cleanly an alkane burns?

shorter chain alkanes burn more cleanly due to higher SA:V ratio

how can you tell if an alkane is burning cleanly?

measure and test the volume of CO2 given off

what is cracking?

• breaking down of long chain hydrocarbons to form a mixture of short chain alkanes and alkenes

why are alkenes useful?

used to make polymers/plastics

why are the molecules produced in cracking not constant?

random bonds are broken - also causes things like hydrogen to be produced

what are the two types of cracking?

• thermal

• catalytic

what are the conditions required for thermal cracking?

• temperature 1000-1200 K

• high pressure 70 atm

• very short time

what does thermal cracking mostly produce?

• shorter chain alkanes

• lots of alkenes

what are the conditions required for catalytic cracking?

• temperature 800-1000k

• slight pressure - 1 / 2 atm

• slightly longer time

• zeolite catalyst

how long can catalytic cracking go on for continuously?

3 years

what does catalytic cracking mostly produce?

• branched chain alkanes

• cycloalkanes

• aromatic hydrocarbons

why is it beneficial to produce branched alkanes?

• straight chain alkanes have a tendency to pre ignite in a combustion engine

• branched chains do not, and burn cleaner

why is it beneficial to produce cyclic hydrocarbons?

• less tendency to pre ignite

• hydrogen gas produced is used in other process

how does an internal combustion engine work?

• small amount of fuel mixed with large excess of air

• mixture ignited with high temperature spark

• explosive burning, forces engine parts to move

• products exit via exhaust

what are the side reactions in an internal combustion engine?

• nitrogen + oxygen → nitrogen (II) oxide

• nitrogen + oxygen → nitrogen (IV) oxide

• sulfur + oxygen → sulfur dioxide

what are all the harmful substances produced by internal combustion engines?

• carbon dioxide

• carbon monoxide

• carbon

• nitrous oxides (N in air)

• sulfur dioxide (fuel impurities)

• hydrocarbons (unburnt fuel)

what is the problem caused by CO2?

global warming

what is the problem caused by CO?

toxic gas

what is the problem caused by carbon?

particles exacerbate asthma

what is the problem caused by NOx?

acid rain and smog

what is the problem caused by SO2?

acid rain

what is the problem caused by hydrocarbons?

react with NOx to form ground level ozone which causes respiratory problems

why is using crude oil bad?

• going to run out

• contributes to pollution

• price always increasing as availability decreases

what can be used to remove air pollutants from exhaust gases from cars?

• catalytic converter

• honeycomb centre covered in catalysts

give equations for the reactions that remove nitrous oxides and carbon monoxide in a catalytic converter

• nitrogen (II) oxide + carbon monoxide → carbon dioxide + nitrogen

• unburnt hydrocarbon + nitrogen (II) oxide → carbon dioxide + nitrogen + water

• nitrogen (II) oxide → nitrogen + oxygen

what is an alternative to crude oil?

biofuel

what is biofuel?

fuel derived from recently living material such as plants or from animal waste

what are some subtypes of biofuels?

• bioethanol

• biodiesel