Fuels and Heats of Reaction
From ZuluNotes - Free Leaving Cert Notes
A fuel is a substance that is changed in some way to produce heat, electricity, or other forms of energy. This is usually by being burnt, although there are exceptions. For this section hydrocarbons are the only fuel you need to be concerned with. They are by far the most common fuel in use today.
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Hydrocarbons
- Hydrocarbons are compounds containing hydrogen and carbon only.
- Sources include petrol, coal and gas.
- The three main types of hydrocarbons are alkanes[1], alkenes[2] and alkynes[3].
Alkanes
- Hydrocarbons in which there are only single bonds between carbon atoms.
| Name | Molecular Formula |
|---|---|
| Methane | CH4 |
| Ethane | C2H6 |
| Propane | C3H8 |
| Butane | C4H10 |
| Pentane | C5H12 |
| Hexane | C6H14 |
| Heptane | C7H16 |
| Octane | C8H18 |
- The structural formula is the formula of a compound showing how atoms are arranged in the molecule.
- A homologous series is a series of compounds of uniform chemical type, showing gradations in physical properties and having a general formula for its members. Each member has a similar method of preparation and each member differs from the previous member by a CH2 unit.
- It is possible for an alkane to be arranged in a ring (cyclohexane).
Isomers
- A condensed structural formula (C4H10) can represent more than one structural formula.
- Isomers are compounds having the same molecular formula but different structures.
- You need not go beyond the isomers of C5H12 for this course.
Naming of Alkanes
- The International Union of Pure and Applied Chemistry have definite guidelines for the naming of organic compounds[5].
- The parent name of the molecule is determined by the number of carbons in the longest chain.
- In the case where two chains have the same number of carbons, the parent is the chain with the most substituents.
- The carbons in the chain are numbered starting from the end nearest the first substituent.
- In the case where there are substituents having the same number of carbons from both ends, numbering starts from the end nearest the next substituent.
- When more than one of a given substituent is present, a prefix is applied to indicate the number of substituents.
- Use di- for two, tri- for three, tetra- for four, etc. and use the number assigned to the carbon to indicate the position of each substituent.
Alkenes
- Hydrocarbons in which there is a double bond between two carbon atoms.
- Alkenes are unsaturated.
- Alkenes are named by taking the corresponding alkane's name and changing the -ane to -ene.
- Similar to cyclohexane, it's possible for an alkene to arrange itself in a ring (cyclohexene).
Naming of Alkenes
- The alkenes have similar systematic names to the alkanes[6].
- The position of the double bond is indicated by which carbon atom it begins at.
Alkynes
- Hydrocarbons in which there is a triple bond between two carbon atoms.
- The alkynes are highly unsaturated due to their carbon triple bond.
- Alkynes are named by taking the corresponding alkane's name and changing the -ane to -yne.
- The only alkyne on the course is ethyne.
- It is a gas used in oxyacetylene welding.
- Mixtures of ethyne and oxygen can reach high temperatures when burned.
Mandatory Experiments
- To prepare ethene and examine its properties
- To prepare ethyne and examine its properties
- To determine the heat of neutralisation of HCl and NaOH[7]
References
- ↑ http://www.chemguide.co.uk/organicprops/alkanemenu.html
- ↑ http://www.chemguide.co.uk/organicprops/alkenemenu.html
- ↑ http://www.ucc.ie/academic/chem/dolchem/html/comp/ethyne.html
- ↑ http://www.sparknotes.com/chemistry/organic2/alkanes/section1.html
- ↑ http://chemistry.about.com/library/weekly/bl052503a.htm
- ↑ http://docbrown.info/page06/AlkeneStructure.htm
- ↑ http://chemistry.slss.ie/ch_mandatoryexperiments.html
