Fuels and Thermochemistry - Leaving Cert HL Chemistry

organic chemistry

the study of compounds of carbon

hydrocarbon

compounds consisting of carbon and hydrogen only

saturated

all carbons are linked by single bonds only

unsaturated

molecules containing double bonds between carbon atoms

homologous series

a series of compounds, all members of which contain the same functional group, have similar properties, and successive members differ by CH2

structural isomer

compounds with the same molecular formula but different structural formulas

aliphatic

organic compound consisting of open chains of carbon atoms and closed ring structures

aromatic

compounds that contain a benzene ring

auto-ignition

the explosion of the petrol-air mixture in an engine before the spark is produced

octane number

thr ability of a fuel to rsist auto-ignition

catalytic cracking

breaking long chain hydrocarbons into shorter chain hydrocarbons

isomerisation

turning long/straight chain hydrocarbons into their isomers

dehydrocyclisation

converts hydrocarbons into ring compounds

adding oxygenates

adding oxygen containing compounds to the fuel

steam reforming

natural gas is mixed with high temperature steam and passed over a catalyst to produce hydrogen and carbon dioxide

CH4 + H2O → 3H2 + CO2

electrolysis

uses electricity to split water into hydrogen and oxygen

2H20 → 2H2 + 02

heat of reaction

the heat change when the number of moles of reactants (indicated by the balanced chemical equation for the reaction) balance completely

heat of combustion

the heat change when one mole of a substance burns completely in excess oxygen

heat of neutralisation

the heat change when one mole of H+ ions from an acid react with one mole of OH- ions from a base

heat of formation

the heat change when one mole of a substance in its standard state is formed from its elements in their standard state

kilogram calorific value

the energy produced when one kilogram of a substance is burned in excess oxygen

bond energy

the average energy required to break one mole of covalent bonds and separate the neutral atoms completely from one another

Hess’ law

if a chemical reaction takes place in a number of stages, the sum of the heat changes in the separate stages is equal to the heat change if the reaction was carried out in one single stage

law of conservation of energy

energy cannot be created or destroyed, but can only be converted from one form of energy to another