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Investigating the heat energy given out by a mole of an alcohol when burning in air.

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Chemistry Coursework – Investigating the heat energy given out by a mole of an alcohol when burning in air.image00.png

First Section: Planning

Aim of the investigation:

The aim of the investigation is to discover the relative amount of heat energy that a set of alcohols release during the combustion process. Then the energy discharged by one mole of that alcohol must be found.

Basic terms:

Exothermic reaction – In an exothermic reaction, the heat energy of the products is less than the heat energy of the reactants. As the reaction occurs, excess heat energy is released and so the energy change between the products and reactants is negative due to the heat being lost. The air near the fuel, rising in temperature, demonstrates this.

Endothermic reaction – In an endothermic reaction, the heat energy of the products is greater than that of the reactants. Heat energy is taken from the surroundings during the reaction and causes the energy change to be positive (heat energy is gained). Thus, the temperature of the air near the burning fuel falls.

Specific Heat Capacity – This is defined as the quantity of energy that is required to raise the temperature of 1kg of a substance by 1 degree Celsius. Its units are J/kgºC. Heat content varies from compound to compound and depends on the physical state of the compound. Here are the specific heat capacities of some other substances and a specific heat energy diagram:

Homologous series – This is a term used to describe members of the same family, which have similar chemical properties and react in a similar fashion as you go down the group. For example, the alkanes group or even the alkali metals in group one.

Structures of alcohols –

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The water will get less heat energy at the end of it all, indicating that it will take longer to raise its temperature.The longer the water takes to heat, the more the mass of the alcohol is lost through burning.

So the alcohol will be involved in more combustion reactions (burning away its mass) if the distance is increased, in order to provide enough heat energy for the water to raise its temperature.

Environmental factors may affect the alcohol’s distribution of heat energy by causing some to be lost to the surroundings. Of these, wind is a prime factor, as it would blow the flame from side to side and away from the can. Excess heat energy from the combustion reaction will be wasted on the air around the system and other objects – hands, table etc. Consequently, the system water will not receive much heat energy and the alcohol will needlessly burn away, releasing heat energy to the wrong place. To sustain a constant flame, heatproof mats (substituting for wind breakers) will be placed at strategic points to ensure that as little disturbance as possible is caused to the system. The air temperature is also an important factor although it is very difficult to control. This is because the hotter the air is, the easier it will be to conduct heat and the less time it will take for the heat to reach the water (do not need to heat up the air to a high temperature but only to. Not to mention that less heat will be lost and the alcohol will not have to burn so much more of itself.

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I have used the following to help me plan my investigation:

I have used the following books to help me plan my investigation:

  • ‘Physics for you’ by Keith Johnson. On page 37 to 39, I found out information concerning measuring heat energy, its values, specific heat capacity and a table displaying specific heat capacities of different substances.
  • ‘Revision guide for GCSE Double Science – Physics’ where on page 67 to 68, there is information about heat transfer, evaporation, the conduction of heat and vibrating particles.
  • ‘Chemistry for you’ by Lawrie Ryan (Revised National Curriculum Edition). On page 178 to 179, there is information regarding organic molecules such as alcohol; their structures, physical properties and homologous series. On page 182, there is information on the combustion of alcohols, a brief explanation of the combustion experiment and combustion formulas. On page 186, which is about energy transfer, there is more detailed coverage of incomplete/complete combustion and fuels. On page 190 to 195, there are things about exothermic/endothermic reactions, what happens to the temperature during these reactions, energy level diagrams, making and breaking bonds and finally bond energy calculations.
  • ‘Nuffield Book of Data’ sheet has exothermic heat energies of all the alcohols combustion reactions and all the varied bond energy values.

I have done the following experiments to help plan my investigation:

  • Experiment on page 191 to see what substances have endothermic or exothermic reactions.
  • Previous practise experiment of the alcohol investigation, which helped me to find corrections for certain procedures, various precautions, tips that would produce less inaccuracy, discover key factors and how to set up the apparatus.

Here is the set up of my results table as an example of what I learnt from the practise experiment:

Omar Baakza                Westminster City School

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