• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

Compare the enthalpy changes of combustion of different alcohols

Extracts from this document...


Task and Aim: Compare the enthalpy changes of combustion of different alcohols. To find the enthalpy changes of combustion of different alcohols and draw conclusions on how these values are affected by their molecular structure. I shall experiment with a minimum of five alcohols. Each alcohol I use will be from the homologous series of primary alcohols, e.g. propan-1-ol or pentan-1-ol. By adding a hydroxyl group on the first carbon each time this ensures that there is only one variable between my 5 alcohols, the carbon chain length. Background Theory and Prediction: Energy changes occur whenever a chemical reaction takes place. A reaction that gives out energy and heats the surroundings is called an exothermic reaction; a reaction that takes in energy and cools the surroundings is called an endothermic reaction. When finding the enthalpy changes of combustion of different alcohols, the chemical reactions that take place will be exothermic. This is because ?H is always -ve and heat is given out to the surroundings. The standard enthalpy change of combustion, ?Hc is the enthalpy change that occurs when 1 mole of a fuel is burned completely in oxygen. In theory, the fuel needs to be burned under standard conditions, 1 atmosphere pressure and 298K. However, in practice this is impossible so I will burn the fuel in the normal way and make the necessary adjustments to allow for non-standard conditions. To measure the enthalpy change we use this relationship: Energy transferred=cm?T Where c is the specific heat capacity of water (4.2J/g) and m is the mass of water used. I predict that as the length of chain of carbons increase in an alcohol, the enthalpy change of combustion will increase e.g. heptan-1-ol will give out more energy than methan-1-ol. I predict this because as more bonds need to be broken and more bonds need to be formed. The intermolecular forces tend to be bigger as the chain increases. ...read more.


I must be extra careful incase the thermometer is filled with mercury as this is a poisonous substance. The calorimeter may also hit the spirit burner which would be extremely dangerous so I must be very sure that the clamps are stable. Bibliography -Teacher Support: Coursework Guidance AS/A Level GCE Chemistry (salters, blue sheet) -Chemical Ideas text book, chapter 4, and 13. -World Wide Web -Teacher support. Start Mass (g) End Mass (g) ? Temp (�C) ? Mass (g) Q (KJ) Mr (g/mol) Moles ? Enthalpy (KJ/mol) Actual ? Enthalpy (KJ/mol) Ratio Methanol 224.70 223.55 17 1.15 14.28 32 0.04 397.36 726 0.55 Repeat 1 223.55 222.28 16 1.27 13.44 32 0.04 338.65 726 0.47 Repeat 2 222.28 221.04 16 1.24 13.44 32 0.04 346.84 726 0.48 Repeat 3 221.04 219.66 16 1.38 13.44 32 0.04 311.65 726 0.43 Average 222.89 221.63 16.25 1.26 13.65 32.00 0.04 348.62 726.00 0.48 Ethanol 221.30 220.28 16 1.02 13.44 46 0.02 606.12 1367 0.44 Repeat 1 220.28 219.20 16 1.08 13.44 46 0.02 572.44 1367 0.42 Repeat 2 219.20 218.15 16 1.05 13.44 46 0.02 588.80 1367 0.43 Repeat 3 218.05 217.10 16 0.95 13.44 46 0.02 650.78 1367 0.48 Average 219.71 218.68 16.00 1.03 13.44 46.00 0.02 604.54 1367.00 0.44 Propan-1-ol 213.42 212.57 16 0.85 13.44 60 0.01 948.71 2021 0.47 Repeat 1 212.58 211.77 16 0.81 13.44 60 0.01 995.56 2021 0.49 Repeat 2 211.77 210.94 16 0.83 13.44 60 0.01 971.57 2021 0.48 Repeat 3 210.94 210.13 16 0.81 13.44 60 0.01 995.56 2021 0.49 Average 212.18 211.35 16.00 0.83 13.44 60.00 0.01 977.85 2021.00 0.48 Butan-1-ol 202.67 201.97 16 0.70 13.44 74 0.01 1420.80 2627 0.54 Repeat 1 201.97 201.24 16 0.73 13.44 74 0.01 1362.41 2627 0.52 Repeat 2 201.24 200.55 16 0.69 13.44 74 0.01 1441.39 2627 0.55 Repeat 3 200.55 199.87 16 0.68 13.44 74 0.01 1462.59 2627 0.56 Average 201.61 200.91 16.00 0.70 13.44 74.00 0.01 1421.80 2627.00 0.54 Pentan-1-ol 195.54 194.85 15 0.69 12.6 88 0.01 1606.96 3331 ...read more.


It was also because of lack of complete combustion that caused the most significant causes to this inaccuracy. This was due to the lack of proper draught exclusion and insulation. To have achieved higher accuracy and precision I might have taped aluminium foil to the heat proof mats. This would have allowed more heat radiation to be deflected onto the water which was where I was trying to divert all the energy towards. The container used to hold the water; the copper calorimeter was metal and would have radiated heat from its entire surface area. A better designed container or a dull outer surface would have minimized this. However when comparing my results to the text book values, I could see that although they were not the same, they were consistently wrong by about 50%. The lack of abnormalities in my results showed that my experiment was carried out using a consistant method which allowed me to better analyse my results. The measures that I kept the same during the experiment were the height of wick and the distance the flame was to the calorimeter. This measurement may not be completely accurate due to possible human error which is why not all my results were dead on 50% but were in the vicinity of this value. Other experimental techniques that I did for all my tests were stirring the water. This allowed the temperature to reach its highest peak using the particle collision theory. Once I stopped the burning, I carried on stirring the water to ensure that the temperature change was accurate in my results. However, as I explained the thermometers used were sometimes ineffective to 1�C. Things I would have changed had I done the experiment again, would be to use a digital thermometer as this would have reduced the possible human errors that I might have done. Also I would have used aluminium foil to reduce loss of heat radiation. ...read more.

The above preview is unformatted text

This student written piece of work is one of many that can be found in our AS and A Level Organic Chemistry section.

Found what you're looking for?

  • Start learning 29% faster today
  • 150,000+ documents available
  • Just £6.99 a month

Not the one? Search for your essay title...
  • Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

See related essaysSee related essays

Related AS and A Level Organic Chemistry essays

  1. Marked by a teacher

    Reactions of aldehydes and ketones. The purpose of this experiment is to compare ...

    5 star(s)

    5. Oxidation with acidified dichromate (VI) solution Aldehyde can be further oxidized to carboxylic acid. The product formed will be a carboxylic acid. In the reduction of dichromate ion, the dichromate ion (orange) is turned to chromium ion (green). Ketone may undergo further oxidation to form carboxylic acid with hot acidified potassium permanganate and under reflux.

  2. Marked by a teacher

    Comparing the enthalpy changes of combustion of different alcohols

    3 star(s)

    * A temperature of 298K (25oC) * Reactants and products in physical states, normal for the above conditions. * A concentration of 1.0mol dm-3 for solutions. Standard enthalpy change of combustion ?Hoc The standard enthalpy change of combustion is the enthalpy change when one mole of an element or compound reacts completely with oxygen under standard conditions.

  1. Comparing The Enthalpy Change OfCombustion Of Different Alcohols

    Enthalpy change when bonds are made (kJ mol-1) Enthalpy of combustion (kJ mol-1) Methanol CH3OH 2808 -3466 -658 Ethanol CH3CH2OH 4728 -6004 -1276 Propan-1-ol CH3CH2CH2OH 6648 -8542 -1894 Butan-1-ol CH3CH2CH2CH2OH 8568 -11080 -2512 Pentanol CH3CH2CH2CH2CH2OH 10488 -13618 -3130 From the table above we can see that as the alcohol becomes

  2. Comparing the enthalpy change of combustion of alcohols down a homologous series.

    in converting reactants, A + B, to products X + Y, is the same regardless of the route by which chemicals change occurs provided the initial and final conditions are the same. Ref. Chemistry in context This is shown below A + B X + Y A + B +

  1. The aim of this experiment is to investigate the enthalpy change of combustion for ...

    The molecule as a whole is said to be polarised. As the dipoles are permanent it can be said that the molecule is permanently polarised. Due to the polarisation of the molecules, alcohols have generally higher boiling and melting points than you might predict points and hence a low volatility and are liquid at room temperature.

  2. Find the enthalpy change of combustion of a number of alcohol's' so that you ...

    I will work out the enthalpy change of combustion by using the fact that 4.2J of energy is required to raise the temperature of 1g of water by 1oc. Apparatus: - * Spirit burner to burn the alcohol (a) Methanol (b)

  1. The Relationship Between The Number of Carbon Atoms In An Alcohol And Its Standard ...

    Dioxide + Water CH3OH + 11/2 O2 CO2 + 2H2O 1 O = O H ----- O ----- H 1/2 O = O H ----- O ----- H 1 O = C = O H | H ----- C ----- O ----- H | H 3 C --- H 1236

  2. The aim of this experiment is to produce Aspirin. This is an estrification in ...

    Normal water will not do because of the impurities in it. * Funnel - This allows hydrochloric acid to be poured into the burette so none is spilt. * Pipette 10cm� - This is used to accurately draw out the correct amount of a substance from a solution.

  • Over 160,000 pieces
    of student written work
  • Annotated by
    experienced teachers
  • Ideas and feedback to
    improve your own work