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

Comparing the enthalpy change of combustion

Extracts from this document...

Introduction

Comparing the enthalpy changes of combustion of different alcohols The aim of this experiment is to investigate how the length of an alcohol molecule and the position of its OH group affect its enthalpy change of combustion. This will be done using the comparison method, using a known value for the enthalpy change of combustion for one fuel (here, propan-1-ol) and replicating the experiment for each alcohol, then accurately comparing the results. The 4 alcohols that will be compared to propan-1-ol (CH3CH2CH2OH) are: o methanol (CH3OH) o ethanol (CH3CH2OH) o propan-2-ol (CH3CH(OH)CH3) o butan-1-ol (CH3CH2CH2CH2OH) The propan-2-ol differs from propan-1-ol because its OH group is positioned on the 2nd carbon atom in the chain. Combustion reactions involve breaking the intra-molecular bonds (bonds between atoms, within the molecule) of a fuel, then making new bonds with oxygen. The formula for the combustion reaction is: Alcohol + Oxygen ==> Carbon Dioxide + Water e.g. CH3OH + 11/2O2 ==> CO2 + 2H2O Breaking bonds takes energy in from the surroundings, and making bonds gives energy back out. The enthalpy change is the net energy transfer of the reaction; it is negative if the reaction is exothermic, like combustion, and positive if the reaction is endothermic. ...read more.

Middle

The final temperature of the water, the temperature change, and the mass of alcohol used may differ. Methanol Ethanol Propan-2-ol Butan-1-ol Molar mass of alcohol g/mol Initial mass of spirit burner g Final mass of spirit burner g Mass of alcohol burned g Moles of alcohol burned mol Initial temperature of water �C Final temperature of water �C Temperature change K Enthalpy change of combustion kJ/mol If time allows, the experiments should be repeated for both the propan-1-ol (to ensure the value for the energy required for rise in water's temperature of 1K is reliable) and for the rest of the alcohols (to ensure the value for the enthalpy change of combustion is reliable). Results Alcohol Methanol Ethanol Propan-1-ol Propan-2-ol Butan-1-ol Initial temperature of water/�C 24 25 23 24 23 Final temperature of water/�C 42 44 44 45 43 Temperature change/�C 18 19 21 21 20 Initial mass of spirit burner/g 176.94 173.99 183.14 201.91 193.77 Final mass of spirit burner/g 175.73 172.84 181.94 200.81 193.01 Change in mass/g 1.21 1.15 1.20 1.10 0.76 The temperatures were measured using a 100�C thermometer, marked every 1�C. The masses were measured using a balance, reading to the nearest 0.1 grams. ...read more.

Conclusion

Although we tried to minimise this heat loss by using heatproof mats, this did not provide the closed environment which would be ideal. It should also be noted that all of the fuels burned with an orange/yellow flame, indicating incomplete combustion. This will have produced less energy than complete combustion, further decreasing the calculated enthalpy change of combustion. If I was to try and improve this experiment, I would use a calorimeter to reduce heat loss. I would also calibrate the equipment using a fuel with a known enthalpy change of combustion, to try and work out how much energy is lost to the equipment. I could then incorporate this into my calculations to give me a more accurate value for the enthalpy change. Sources Salters Advanced Chemistry, Chemical Storylines, Heinemann, 2000, pg 22. Salters Advanced Chemistry, sheets DF1.2 and DF1.3, 2000. Chemistry in Context, Nelson, 4th Edition, 1995, pg 450. These are reliable sources as they are respected and widely used textbooks and course materials. CLEAPSS Science Publications CD-ROM, 2005. CLEAPSS hazcards are usid in school laboratories. http://www.wpbschoolhouse.btinternet.co.uk/page18/02DFws.htm 6/11/2007 I believe this is reliable as it has been designed to help with the Salters AS course. http://www.chemicool.com/forum/post-177.html 11/11/2007 I believe this is reliable as there are other posts on the forum, by the same member, which I know are correct. ?? ?? ?? ?? Sophie Catt ...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. The aim of this experiment is to investigate the enthalpy change of combustion for ...

    4CO2(g) + 5H2O(g) =9(C-H) + 3(C-C) + C-O + O-H + 6(O=O) =8(C=O) + 10(H-O) =9(410) + 3(350) + 360 + 460 + 6(496) =8(740) + 10(460) =3690 + 1050 + 360 + 460 + 2976 =5920 + 4600 =+8536KJ/mol (bonds broken) =-10520KJ/mol H =+8536-10520 =-1984KJ/mol Due to Butan-1-ol and Butan-2-ol having the same

  2. Comparing The Enthalpy Change OfCombustion Of Different Alcohols

    energy loss from the evaporation of water due to the experiments being heated to approximately 85 degrees Celsius each time. The figure for the enthalpy change of combustion was negative because the reaction was endothermic. This is also proved by my results as they are negative.

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

    take the initial temperature of the water and initial mass of the alcohol I will then burn the alcohol until an increase in temperature of 20oc has occurred in the water I will then reweigh the alcohol. The measurements * Mass of alcohol burned (g)

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

    * The capillary tube was placed in the melting point apparatus and the crystals were observed through a magnifying glass of the apparatus. * The range at which the aspirin melted was noted. The experiment was then repeated for pure aspirin. Results Compound Melting temperature (c) Re-crystalised aspirin 130-135 (c)

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

    Therefore, if the bond energies for these extra atoms are added to the previous alcohol, the ?H can be found out for the next alcohol. Below are the bond energies that are inputted into the previous alcohols to work out the ?H of the next alcohol.

  2. Comprehensive and Detailed Chemistry notes

    * identify that ethylene serves as a monomer from which polymers are made -- Ethylene is an important monomer. -- Ethylene undergoes addition polymerisation to form polyethylene. -- In this process the double bond breaks LDPE: -- It is made undre high pressures and temperatures -- An initiator such as

  1. Compare the enthalpy changes of combustion of different alcohols

    The reason for this is due to the added hydroxyl group (-OH), this means that one of the bonds of oxygen has already been made so there is less energy needed as there are less bonds to be broken. This is the same for both Propane/Propanol and Octane/Octanol.

  2. Experiment Hypothesis: The energy released by an alcohol increases as the number of carbon ...

    This is because if the distance is increased, it would take more time to heat up the water, thus recording a low temperature rise and if increased high temperature rise would be recorded. Thus for a matter of consistency it was kept constant throughout the reaction.

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