Properties of different alcohols used as fuels.

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TITLE: COMBUSTION OF ALCOHOLS AS FUELS.

  • DESIGN

Question: How is enthalpy change affected by the molecular structure of alcohols and which is comparatively a more suitable fuel?

The hypothesis I will be making is that the enthalpy of combustion of the alcohols will increase as the length of the alcohol chain increases i.e. the addition of a CH2 group. In a chemical reaction, the bonds between atoms in the reactant side break down to form new bonds in the products. When alcohols are combusted, the covalent bonds break up to form new bonds. The energy released when bonds are formed is more than the energy absorbed when bonds are broken which implies that enthalpy change reactions are exothermic reactions since heat is given out and therefore the value of the enthalpy change will be negative. Therefore, when there are more atoms, more bonds are broken and hence more bonds are made. Enthalpy change of combustion of alcohols is therefore affected by molecular structure as it takes more energy to break and make bonds when the number of atoms is increases than the energy needed when the number of atoms is comparatively lower. Finally, the fuel that has the highest enthalpy change should be comparatively more effective as a fuel.

Variables:

  • Independent variables:
  1. Propanol
  2. Butanol
  3. Pentanol
  4. Hexanol

  • Dependent variables:

  • Controlled variables:

  1. Change in temperature of water which is = 30˚C.

  1. Volume of distilled water which is heated = 50cm³.

  1. There should be a constant distance between the base of the copper calorimeter and the spirit lamp otherwise different amount of energy could escape each time giving us inaccurate results. The distance between the tip of the wick of the sprit lamp and the base of the calorimeter should be 5cm.

  1. In order to avoid excessive heat loss, the same calorimeter should be used throughout the experiment.
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Apparatus required:

  1. 100cm³ beaker.
  2. Copper calorimeter and stirrer.
  3. Digital balance.
  4. Thermometer.
  5. Clamp Stand to hold the calorimeter.
  6. Scale to measure distance between tip of wick and base of calorimeter.
  7. Matches to ignite the wick of the spirit lamps.
  8.  Alcohols in spirit burner:
  • Propanol.
  • Butanol.
  • Pentanol.
  • Hexanol.
  1. Distilled water = 50cm³

Method:

  1. Measure 50 cm³ of distilled water in the beaker and pour it into the calorimeter.
  2. Measure the mass of the spirit lamp on the digital balance.
  3. Record the temperature of the water using a thermometer.
  4. Keep ...

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