The Combustion of Alcohols and the factors affecting these reactions

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The Combustion of Alcohols and the factors affecting these reactions

Planning

Aim:

The aim of this experiment is to investigate the combustion of alcohols and how the different structures of alcohols affect the amount of energy given off.

Alcohols:

The general formula is CnH2n+1OH and n representing the number of carbon atoms in an alcohol molecule. So if I know the number of carbon atoms present this formula allows me to find the formula for every alcohol. From the simplest alcohol methanol, that has one carbon molecule, to pentanol with five carbon atoms. Throughout the combustion of the alcohols, the alcohols will react with the oxygen in the air. The word equation below represents this:

Alcohol + Oxygen Carbon Dioxide + Water

The table below shows the alcohols I will be using in this investigation:

To show the structure of these alcohols I am using the following diagrams illustrate this:

Variables:

There are a number of variables that I have to consider in this investigation. Variables are factors which will have an effect on the results of the experiment. It is important to keep most of the variables constant or “controlled”, they do not change, to ensure a fair test. The controlled variables are: the height of the calorimeter above the spirit burner, the material of the calorimeter, the change in temperature, the amount of water, the size of the copper calorimeter and the size of the wick, which was easily chosen as only one size was available. The rise in temperature was decided to be a 15˚C increase from the difference of the initial and final temperature, because it did not take a long time to reach this temperature and the dependant variable would still change clearly

The independent variable is the variable that is changed to affect the dependant variable. The independent variable is the size of alcohol used or the number of carbon atoms (which determines the alcohol). The dependant variable is the variable that changes depending on the independent variable, which is the change in mass. This is used to calculate the energy released in the reaction.

Preliminaries:

The reason of doing a preliminary was to confirm the decisions made on the controlled variables, to see that a reasonable mass difference occurred and if not the independent variable which has to be increased on decreased.

A clamp was set up; holding the copper calorimeter containing 100cm³ of water, and a thermometer was placed in the water. A spirit burner with the correct alcohol was placed underneath the calorimeter was positioned, the wick was set alight and heated the water above in the calorimeter. I experimented with the temperature change at 15˚C there was a sufficient amount of mass difference in the burner. Therefore, 15˚C rise in temperature was correct decision.

These are the results of the preliminaries:

Predictions:

Chemical energy is stored within the chemical bonds, the amount of all the energy within a substance is known as the enthalpy. During the combustion reaction, the alcohol is converted into carbon dioxide and water. However, excess energy is created, in the form of heat this is released into the environment. Reactions where the energy of the reactants (alcohol and oxygen) is more than the energy of the products (carbon dioxide and water) are known as exothermic reactions. Reactions where the energy of the reactants is less than the energy of the products are known as endothermic reactions.

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I predict that the larger the molecule the more bonds there are to make and break. More energy has been used to break bonds; more energy would also be given out when making the bonds of the products of the reaction. It is possible to suggest that the amount of energy given off by an alcohol with a larger carbon chain (more carbon atoms) will be larger than an alcohol with a smaller carbon chain, for example, Butanol has twice as many carbon atoms as Ethanol, therefore there should be twice as much as energy given out by Butanol ...

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