Chapter 21: Fuels and Heats of Reaction Flashcards
Organic Chemistry
Is the study of the compounds of carbon
Hydrocarbon
A compound that contains hydrogen and carbon only
Fossil fuels
Are fuels that were formed from the remains of plants and animals that lived millions of years ago.
Saturated compound
A saturated compound is one in which there are only single bonds between the atoms in the molecule.
A homologous series
is defined as;
- A series of compounds of similar chemical properties
- Showing gradation in physical properties
- Having a general formula for its members
- Each member having a similar method of preparation
- Each member differing from the previous member by a CH2 unit.
Structural Isomers
are compounds with the same molecular formula but different structural formulas.
Unsaturated compound
An unsaturated compound is one that contains one or more double or triple bonds between the atoms in the molecule.
An aliphatic compound
is an organic compound that consists of open chains of carbon atoms and closed chain compounds that resemble them in chemical properties.
Aromatic compounds
are compounds that contain a benzene ring structure in their molecules
Auto-ignition
is premature ignition of the petrol-air mixture before normal ignition of the mixture by a spark takes place.
Sources of hydrocarbons;
- Coal
- Natural gas (methane)
- Petroleum (crude oil)
Alkane formula
Cn H2n + 2
Alkene formula
Cn H2n
Alkyne formula
Cn H2n - 2
Fractional Distillation process
1) Crude oil is heated in a furnace.
2) Hot crude oil mixture enters the bottom of the fractionating column which contains a series of trays to collect the condensed liquid.
3) Substances with higher boiling points condense in the lower part of the fractionating column.
4) Substances with lower boiling points condense in the higher part of the fractionating column.
Octane Number
The octane number of a fuel is a measure of the tendency of the fuel to resist knocking.
Factors affecting octane number
1) Length of chain: the shorter the alkane chain, the higher the octane number.
2) Degree of branching: the more branched the chain, the higher the octane number.
3) Straight chain or cyclic structure: Cyclic compounds have a higher octane number than straight chain compounds.
Ways of increasing the octane number of petrol
- Isomerisation
- Catalytic cracking
- Dehydrocyclisation
- Adding oxygenates
Catalytic cracking
is the breaking down of long-chain hydrocarbon molecules by the action of heat and catalysts into short-chain molecules for which there is greater demand.
Heat of reaction
is the heat change when the numbers of moles of reactants indicated in the balanced equation for the reaction react completely.
Heat of combustion
The heat of combustion of a substance is the heat change when one mole of the substance is completely burned in excess oxygen.
Bond energy
the average energy required to break one mole of a particular covalent bond and to separate the neutral atoms completely from each other.
Heat of neutralisation
is the heat change when one mole of H+ ions from an acid reacts with one mole of OH- ions from a base.
Heat of formation
The heat of formation of a compound is the heat change that takes place when one mole of a compound in its standard state is formed from its elements in their standard states.
