Fuels, Hydrocarbons, Homologous Series

Fuels

• A fossil fuel is formed from the remains of living organisms.
• The most common fossil fuels are coal, oil, and gas.
• A fraction is a group of compounds with similar boiling points.

Properties of Fractions

Combustion

• Complete combustion of a hydrocarbon produces carbon dioxide and water.
• Combustion gives out energy.

Exothermic vs. Endothermic Reactions

• Exothermic: Any reaction or process which gives out energy.
• Endothermic: Any reaction or process which takes in energy.

Energy from Fuels

• Units for energy: Joules (J) or Kilojoules (kJ)
• 1 kJ = 1000 J

Specific Heat Capacity

• Specific heat capacity of water: 4.18 kJ/kg \degree C
• Formula: E = mc \Delta T
  • E: Energy gained by the water (in kJ)
  • c: Specific heat capacity of water (4.18 kJ/kg \degree C)
  • m: Mass of water heated (in kg). Note: 1 ml = 1 cm^3, 1 cm^3 = 1 g
  • \Delta T: Change in temperature of water (in degree C)

Structure of Hydrocarbons

• A hydrocarbon is a compound which contains carbon and hydrogen only.

Examples

• Methane: CH_4

  • Full structural formula:

   H
   | 
  H-C-H
   | 
   H
  

• Ethane: C2H6

  • Full structural formula:

   H  H
   |  |
  H-C-C-H
   |  |
   H  H
  

  • Shortened structural formula: CH3CH3

Naming Conventions

• meth- = 1 carbon
• eth- = 2 carbons
• prop- = 3 carbons
• but- = 4 carbons
• pent- = 5 carbons
• hex- = 6 carbons
• hept- = 7 carbons
• oct- = 8 carbons
• non- = 9 carbons
• dec- = 10 carbons

Alkanes

• Alkanes end in "-ane".
• General formula: CnH{2n+2}

Homologous Series

• A homologous series is a family of compounds which have the same general formula and similar chemical properties.

Examples and Properties

Energy Release Experiment Problems

1. Lots of heat energy is lost to the surrounding air and to the apparatus.
2. Alcohol is burning with a yellow sooty flame, which means it is not burning efficiently (incomplete combustion), therefore not giving out maximum heat energy.

Saturation

• Hydrocarbons with only single bonds between the carbon atoms are saturated; therefore, alkanes are saturated.

Alkenes

• Alkenes end in "-ene".
• General formula: CnH{2n}
• Hydrocarbons with double bonds between the carbon atoms are unsaturated; therefore, alkenes are unsaturated.

Cycloalkanes

• The first member is cyclopropane.

  H
  | 
C-H
 / \
HC C-H
  \ /
   H

• General formula: CnH{2n}
• Cycloalkanes are saturated.

Reactions with Bromine Water

• Alkanes do not decolourise bromine water.
• Alkenes do decolourise bromine water. This is called an addition reaction.

Hydrogenation and Hydration

• Hydrogenation: When hydrogen is added to an alkene to make an alkane.
• Hydration: When water is added to an alkene to make an alcohol.

Isomers

• Molecules with the same molecular formula but different structural formulas.

Alcohols

• Contain a hydroxyl group (-OH).
• End in "-ol".

Example: Ethanol

  H   H
  |   |
H-C-C-OH
  |   |
  H   H

Carboxylic Acids

• Contain a carboxyl group (-COOH).
• Shortened formula: CH_3COOH

Esters

• Formed when an alcohol and a carboxylic acid react to create an ester.