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# In my investigation I will measure the heat given out by different types of primary alcohols when combusting with oxygen and compare the difference in the energy out put per mole of different alcohols.

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Introduction

GCSE CHEMISTRY COURSEWORK

Aim:

In my investigation I will measure the heat given out by different types of primary alcohols when combusting with oxygen and compare the difference in the energy out put per mole of different alcohols.

Hypotheses

Before we can have a look at the heat content of the different alcohols, we must be able to understand the process of combustion, the changes of the energy within the system while combusting with oxygen and how to determine the difference of the energy given out per unit.

First it is crucial to know that it is the external energy that we are measuring of the system, because as the Second Law of thermodynamics states that heat cannot be completely converted into work without some part of the system undergoing change, a equation is applied to the law illustrates that H (total heat content) = G (free energy) + TS (temperature×entropy, TS is the unfree energy which is associated with the degree of disorder of the system), and H can only be equal to G when TS=0 which only takes place at the temperature of absolute zero. We therefore cannot measure the total change in enthalpy (total heat content) since the 3rd law of thermodynamics states that absolute zero cannot be reached; the entropy which measures the degree of disorder also increases spontaneously that the particles of the system become disorderer or more random. What this investigation measures is the spontaneous change in the free energy which is converted into heat as stated in the second law of thermodynamics.

Then it is necessary to know that the reaction is exothermic that is heat

Middle

Tin canHeat proof mat

(See photo 1)

Method

In order to carry out this investigation, two measurements must be taken; they are the loss in the weight of the alcohols, and the temperature change of the water. Subsequently before we can start the experiment we must measure the weight of the spirit burner, and record the reading. Then the stand boss and the clamp should be set up to fix the tin in place. The reason why I have chosen the tin to be the calorimeter is because it is a good conductor to heat thus it has a relatively low heat capacity, and more kinetic energy can be passed to the water molecules efficiently to make accurate my results. The spirit burner should be positioned directly beneath the tin and a heat proof mat is needed to be placed under the spirit burner. The distance between the peak of the wick and the bottom of the tin must be kept constant in order to carry out a fair comparison. A draught shield is needed to be placed around the spirit burner and the tin to prevent the unnecessary heat loss that could vary the result of the experiment. (See photo 2) After the apparatus have been set up as described above, then we must measure 200ml of water of 2×100ml measuring cylinder and add which to the tin, and then place the thermometer to the water and wait until the reading is stable. It important to keep the volume of water constant since the energy required to raise 1oc is associated with the mass. This stable reading can give the actual temperature

Conclusion

As well as to discover the pattern among the primary alcohols, secondary and tertiary alcohols can also be investigated. We already know the relationship between the numbers of carbon atoms or the length of the carbon chain and the energy output, it would be equally significant to learn the science when the carbons are not in a chain or a irregular chain, and how a hybridized carbon if any at all is able to alter the results. Investigations could be among propan-2-ol, butan-2-ol, pentan-2-ol, hexan-2-ol, cyclohexanol and 2-methyl-propan-2-ol.

Coursework completed by Lu Xiao (Adrian) in November 2002-12-2

Bibliography: “Advancing Chemistry” of Oxford University Press by Michael Lewis and Guy Waller, “Chemistry for you” by Lawrie Ryan, “Chemistry, a practical approach” by , and “www.creative-chemistry.org”

Acknowledgements from D.G.Galbreath PhD and Mr. S.D.Penthreath M.A.

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